Strange PANIC in gwlib/conn.c

Hi guys,

 I have a strange crash in my application that uses gwlib (from 1.4.2). Every so often, we see:

PANIC: gwlib/thread.c:139: mutex_lock_real: Mutex failure! (Called from gwlib/conn.c:202:lock_out.)

or 

PANIC: gwlib/conn.c:200: lock_out: Assertion `gwthread_self() == conn->claiming_thread' failed.

Now, the most we are doing is receiving http calls or making http calls. Multi-threaded of course. This error occurs under load. Any ideas why these would happen?

Much appreciated.

Paul.