On a server running with key_cache_segments != 0, doing an INSERT on a MyISAM table and at the same time a SET GLOBAL key_buffer_size or key_cache_block_size (might probably also happen with other variables) with any value => the INSERT query will never end and won't be killable (will stay in killed state but table lock and process will still be active).

In order to unlock the table, mysqld must be SIGKILL and the table will be crashed at restart.

ps: I only have tried with INSERT and SELECT, using a SELECT doesn't triggers the bug.