GDB does not step into or over "sleep" function

[Denset dot Serralta at radisys dot com]

We are using GDB 4.18 on an NT host to debug target software running on a
PowerPC based adapter. We are using a function called ProcessSleep which is
a call to our kernel.  It basically allocates a semaphore, blocks on it
subject to a user specified timeout and then returns the semaphore.One
problem we can't seem to get around though is that if the process being
debugged makes a 'ProcessSleep' call, the debugger never gains control when
we step over it.  Even if we set a breakpoint past the call and let it run,
it never returns.  A status utility that we have shows the process as
queued, but we never regain control.  Does anybody know any reason(s) why
this should happen.