diff --git a/src/core.c b/src/core.c
index d588bb5c..cba3f642 100644
--- a/src/core.c
+++ b/src/core.c
@@ -8416,7 +8416,7 @@ __hot static int page_touch(MDBX_cursor *mc) {
     np->mp_txnid = txn->mt_front;
     return MDBX_SUCCESS;
   }
-  tASSERT(txn, !IS_OVERFLOW(mp));
+  tASSERT(txn, !IS_OVERFLOW(mp) && !IS_SUBP(mp));
 
   if (IS_FROZEN(txn, mp)) {
     /* CoW the page */
@@ -16102,8 +16102,12 @@ __hot static __always_inline int page_get_checker_lite(const uint16_t ILL,
 
   if (((ILL & P_OVERFLOW) || !IS_OVERFLOW(page)) &&
       (ILL & (P_BRANCH | P_LEAF | P_LEAF2)) == 0) {
-    if (unlikely(page->mp_upper < page->mp_lower ||
-                 ((page->mp_lower | page->mp_upper) & 1) ||
+    /* Контроль четности page->mp_upper тут либо приводит к ложным ошибкам,
+     * либо слишком дорог по количеству операций. Заковырка в том, что mp_upper
+     * может быть нечетным на LEAF2-страницах, при нечетном количестве элементов
+     * нечетной длины. Поэтому четность page->mp_upper здесь не проверяется, но
+     * соответствующие полные проверки есть в page_check(). */
+    if (unlikely(page->mp_upper < page->mp_lower || (page->mp_lower & 1) ||
                  PAGEHDRSZ + page->mp_upper > txn->mt_env->me_psize))
       return bad_page(page,
                       "invalid page' lower(%u)/upper(%u) with limit %zu\n",
@@ -18082,9 +18086,9 @@ static __hot int cursor_put_nochecklen(MDBX_cursor *mc, const MDBX_val *key,
                          mc->mc_xcursor->mx_dbx.md_klen_min =
                              mc->mc_xcursor->mx_dbx.md_klen_max =
                                  data->iov_len);
+      if (mc->mc_flags & C_SUB)
+        npr.page->mp_flags |= P_LEAF2;
     }
-    if ((mc->mc_db->md_flags & (MDBX_DUPSORT | MDBX_DUPFIXED)) == MDBX_DUPFIXED)
-      npr.page->mp_flags |= P_LEAF2;
     mc->mc_flags |= C_INITIALIZED;
   }
 
@@ -18361,7 +18365,11 @@ static __hot int cursor_put_nochecklen(MDBX_cursor *mc, const MDBX_val *key,
           if (unlikely(fp_flags & P_LEAF2)) {
             memcpy(page_data(mp), page_data(fp),
                    page_numkeys(fp) * fp->mp_leaf2_ksize);
+            cASSERT(mc,
+                    (((mp->mp_leaf2_ksize & page_numkeys(mp)) ^ mp->mp_upper) &
+                     1) == 0);
           } else {
+            cASSERT(mc, (mp->mp_upper & 1) == 0);
             memcpy(ptr_disp(mp, mp->mp_upper + PAGEHDRSZ),
                    ptr_disp(fp, fp->mp_upper + PAGEHDRSZ),
                    olddata.iov_len - fp->mp_upper - PAGEHDRSZ);
@@ -18979,6 +18987,7 @@ __hot static int __must_check_result node_add_leaf2(MDBX_cursor *mc,
   const size_t ksize = mc->mc_db->md_xsize;
   cASSERT(mc, ksize == key->iov_len);
   const size_t nkeys = page_numkeys(mp);
+  cASSERT(mc, (((ksize & page_numkeys(mp)) ^ mp->mp_upper) & 1) == 0);
 
   /* Just using these for counting */
   const intptr_t lower = mp->mp_lower + sizeof(indx_t);
@@ -18998,6 +19007,8 @@ __hot static int __must_check_result node_add_leaf2(MDBX_cursor *mc,
     memmove(ptr_disp(ptr, ksize), ptr, diff * ksize);
   /* insert new key */
   memcpy(ptr, key->iov_base, ksize);
+
+  cASSERT(mc, (((ksize & page_numkeys(mp)) ^ mp->mp_upper) & 1) == 0);
   return MDBX_SUCCESS;
 }
 
@@ -19164,6 +19175,7 @@ __hot static void node_del(MDBX_cursor *mc, size_t ksize) {
     mp->mp_lower -= sizeof(indx_t);
     cASSERT(mc, (size_t)UINT16_MAX - mp->mp_upper >= ksize - sizeof(indx_t));
     mp->mp_upper += (indx_t)(ksize - sizeof(indx_t));
+    cASSERT(mc, (((ksize & page_numkeys(mp)) ^ mp->mp_upper) & 1) == 0);
     return;
   }
 
@@ -20830,8 +20842,7 @@ __cold static int page_check(const MDBX_cursor *const mc,
     break;
   }
 
-  if (unlikely(mp->mp_upper < mp->mp_lower ||
-               ((mp->mp_lower | mp->mp_upper) & 1) ||
+  if (unlikely(mp->mp_upper < mp->mp_lower || (mp->mp_lower & 1) ||
                PAGEHDRSZ + mp->mp_upper > env->me_psize))
     rc = bad_page(mp, "invalid page lower(%u)/upper(%u) with limit %zu\n",
                   mp->mp_lower, mp->mp_upper, page_space(env));
@@ -20847,11 +20858,6 @@ __cold static int page_check(const MDBX_cursor *const mc,
           bad_page(mp, "%s-page nkeys (%zu) < %u\n",
                    IS_BRANCH(mp) ? "branch" : "leaf", nkeys, 1 + IS_BRANCH(mp));
   }
-  if (!IS_LEAF2(mp) && unlikely(PAGEHDRSZ + mp->mp_upper +
-                                    nkeys * sizeof(MDBX_node) + nkeys - 1 >
-                                env->me_psize))
-    rc = bad_page(mp, "invalid page upper (%u) for nkeys %zu with limit %zu\n",
-                  mp->mp_upper, nkeys, page_space(env));
 
   const size_t ksize_max = keysize_max(env->me_psize, 0);
   const size_t leaf2_ksize = mp->mp_leaf2_ksize;
@@ -20860,8 +20866,20 @@ __cold static int page_check(const MDBX_cursor *const mc,
                  (mc->mc_db->md_flags & MDBX_DUPFIXED) == 0))
       rc = bad_page(mp, "unexpected leaf2-page (db-flags 0x%x)\n",
                     mc->mc_db->md_flags);
-    if (unlikely(leaf2_ksize < 1 || leaf2_ksize > ksize_max))
-      rc = bad_page(mp, "invalid leaf2-key length (%zu)\n", leaf2_ksize);
+    else if (unlikely(leaf2_ksize != mc->mc_db->md_xsize))
+      rc = bad_page(mp, "invalid leaf2_ksize %zu\n", leaf2_ksize);
+    else if (unlikely(((leaf2_ksize & nkeys) ^ mp->mp_upper) & 1))
+      rc = bad_page(
+          mp, "invalid page upper (%u) for nkeys %zu with leaf2-length %zu\n",
+          mp->mp_upper, nkeys, leaf2_ksize);
+  } else {
+    if (unlikely((mp->mp_upper & 1) || PAGEHDRSZ + mp->mp_upper +
+                                               nkeys * sizeof(MDBX_node) +
+                                               nkeys - 1 >
+                                           env->me_psize))
+      rc =
+          bad_page(mp, "invalid page upper (%u) for nkeys %zu with limit %zu\n",
+                   mp->mp_upper, nkeys, page_space(env));
   }
 
   MDBX_val here, prev = {0, 0};
@@ -20869,7 +20887,7 @@ __cold static int page_check(const MDBX_cursor *const mc,
     if (IS_LEAF2(mp)) {
       const char *const key = page_leaf2key(mp, i, leaf2_ksize);
       if (unlikely(end_of_page < key + leaf2_ksize)) {
-        rc = bad_page(mp, "leaf2-key beyond (%zu) page-end\n",
+        rc = bad_page(mp, "leaf2-item beyond (%zu) page-end\n",
                       key + leaf2_ksize - end_of_page);
         continue;
       }
@@ -20878,7 +20896,7 @@ __cold static int page_check(const MDBX_cursor *const mc,
         if (unlikely(leaf2_ksize < mc->mc_dbx->md_klen_min ||
                      leaf2_ksize > mc->mc_dbx->md_klen_max))
           rc = bad_page(
-              mp, "leaf2-key size (%zu) <> min/max key-length (%zu/%zu)\n",
+              mp, "leaf2-item size (%zu) <> min/max length (%zu/%zu)\n",
               leaf2_ksize, mc->mc_dbx->md_klen_min, mc->mc_dbx->md_klen_max);
         else
           mc->mc_dbx->md_klen_min = mc->mc_dbx->md_klen_max = leaf2_ksize;
@@ -20887,7 +20905,7 @@ __cold static int page_check(const MDBX_cursor *const mc,
         here.iov_base = (void *)key;
         here.iov_len = leaf2_ksize;
         if (prev.iov_base && unlikely(mc->mc_dbx->md_cmp(&prev, &here) >= 0))
-          rc = bad_page(mp, "leaf2-key #%zu wrong order (%s >= %s)\n", i,
+          rc = bad_page(mp, "leaf2-item #%zu wrong order (%s >= %s)\n", i,
                         DKEY(&prev), DVAL(&here));
         prev = here;
       }
@@ -21299,6 +21317,8 @@ static int page_split(MDBX_cursor *mc, const MDBX_val *const newkey,
   DKBUF;
 
   MDBX_page *const mp = mc->mc_pg[mc->mc_top];
+  cASSERT(mc, (mp->mp_flags & P_ILL_BITS) == 0);
+
   const size_t newindx = mc->mc_ki[mc->mc_top];
   size_t nkeys = page_numkeys(mp);
   if (AUDIT_ENABLED()) {
@@ -21414,6 +21434,15 @@ static int page_split(MDBX_cursor *mc, const MDBX_val *const newkey,
         if (page_room(mn.mc_pg[ptop]) < branch_size(env, &sepkey))
           split_indx = minkeys;
       }
+      if (foliage) {
+        TRACE("pure-left: foliage %u, top %i, ptop %zu, split_indx %zi, "
+              "minkeys %zi, sepkey %s, parent-room %zu, need4split %zu",
+              foliage, mc->mc_top, ptop, split_indx, minkeys,
+              DKEY_DEBUG(&sepkey), page_room(mc->mc_pg[ptop]),
+              branch_size(env, &sepkey));
+        TRACE("pure-left: newkey %s, newdata %s, newindx %zu",
+              DKEY_DEBUG(newkey), DVAL_DEBUG(newdata), newindx);
+      }
     }
   }
 
@@ -21459,6 +21488,7 @@ static int page_split(MDBX_cursor *mc, const MDBX_val *const newkey,
         mp->mp_lower += sizeof(indx_t);
         cASSERT(mc, mp->mp_upper >= ksize - sizeof(indx_t));
         mp->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
+        cASSERT(mc, (((ksize & page_numkeys(mp)) ^ mp->mp_upper) & 1) == 0);
       } else {
         memcpy(sister->mp_ptrs, split, distance * ksize);
         void *const ins = page_leaf2key(sister, distance, ksize);
@@ -21471,6 +21501,8 @@ static int page_split(MDBX_cursor *mc, const MDBX_val *const newkey,
         sister->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
         cASSERT(mc, distance <= (int)UINT16_MAX);
         mc->mc_ki[mc->mc_top] = (indx_t)distance;
+        cASSERT(mc,
+                (((ksize & page_numkeys(sister)) ^ sister->mp_upper) & 1) == 0);
       }
 
       if (AUDIT_ENABLED()) {