threadDelay not ending

[Rich Fought]

I've got some unit test code that forks off test processes using the 
'system' function and then delays using 'threadDelay' to synchronize 
with the test process.

This has worked fine until I upgraded to 6.4.2, now some of the 
'threadDelay' calls never return - it's like they are stuck in limbo.

Any ideas?  What would have changed between 6.4 and 6.4.2 that would 
cause this behavior?

Thanks,
Rich