I found this while trying to workaround MDEV-6488.
There are 3 things to note:
1) The table structure (DESC x) is correct, but SELECT x returns only empty fields, without a good reason.
2) If you remove the TEMPORARY keyword, the output will be different: we get 0 rows without a good readon.
3) If you remove TEMPORARY and uncomment the SET statement, the behaviour is correct (no bug). But "x" is not a special char...
I still couldn't find any way to create a temporary CONNECT table with a procedure.