X found bug in wc 1 invalidation

bigfile/file_zodb.py

@@ -143,6 +143,11 @@ class ZBlkBase(Persistent):
 
     # DB notifies this object has to be invalidated
     # (DB -> invalidate .blkdata -> invalidate memory-page)
+    #
+    # FIXME this assumes that ZBlk always stays associated with #blk, not moved
+    #       and never e.g. deleted from bigfile. However it is NOT correct: e.g
+    #       ZBigFile.storeblk() can change type of stored zblk - i.e. it rewrites
+    #       ZBigFile.blktab[blk] with another ZBlk created anew.
     def _p_invalidate(self):
         # do real invalidation only once - else we already lost ._v_zfile last time
         if self._p_state is GHOST: