PHP: Error in my_thread_global_end(): 1 threads didn't exit

Whenever a new thread is created libmysql is told about that by Windows. It then
increases a thread counter and initializes some data. When libmysql is being unloaded
it checks whether all threads have finished, if not it tries to tell them "close now"
and gives them 5 seconds for that. In general this works in a nice way.