Statements with CONNECTION_ID were forced to be kept in the transactional
cache and by consequence non-transactional changes that were supposed to
be flushed ahead of the transaction were kept in the transactional cache.

This happened because after BUG#51894 any statement whose thd's
thread_specific_used was set was kept in the transactional cache. The idea
was to keep changes on temporary tables in the transactional cache. However,
the thread_specific_used was set not only for statements that accessed
temporary tables but also when the CONNECTION_ID was used.

To fix the problem, we created a new variable to keep track of updates
to temporary tables.