Signals and an exiting thread

We're trying to control one process from another process through
signals (I know, revolutionary ;-), and we've found that a signal
occasionally gets lost.  The process we're signaling is
multi-threaded.  It looks like the signal is lost when the kernel
decides to post the signal to a thread that is in the process of dying
(calling pthread_exit, etc).

Is this expected behavior that we should just handle, or is it a race
in the kernel that should be/will be/already is fixed?

It may be that a fix is already in current, and I just haven't found
it in my searches through the source code (I'm working off of source
code for an older 8.0 image).  If it is fixed, I'd appreciate a
pointer to the code that fixes it.

Thanks in advance for the help
- Justin