pseudo_thread_id was reset to zero via mysql_change_user() handling
whereas there is no reason to do that.  Moreover, having two
concurrent threads that change user and create a namesake temp tables
leads to recording the dup pair of queries:

   set @@session.pseudo_thread_id = 0;
   CREATE temporary table `the namesake`;

which will stall the slave as the second instance can not be created.
And that is the bug case.

Fixed by correcting pseudo_thread_id value after mysql_change_user().