connections
The problem is that tables can enter open table cache for a thread without 
being properly cleaned up. This can happen if make_join_statistics() fails 
to read a const table because of e.g. a deadlock. It does set a member of 
TABLE structure to a value it allocates, but doesn't clean-up this setting 
on error nor does it set the rest of the members in JOIN to allow for 
automatic cleanup.
As a result when such an error occurs and the next statement depends re-uses 
the table from the open tables cache it will get it with this 
TABLE::reginfo.join_tab pointing to a memory area that's freed.
Fixed by making sure make_join_statistics() cleans up TABLE::reginfo.join_tab 
on error.