gdb attach detach - strange behaviour on RHEL 3.0
 

A thread in my process blocks (condWait) on a mutex indefinately because of bug. But When I attach this process (in blocked state) to gdb & detach it, blocked thread starts execution & exits successfully.
What would be the reason for this abrupt behaviour?
What does gdb detach do? which signals does it send?
Note : If i dont attach blocked process to gdb, thread blocks on that mutex indefinately due to bug.