Signal Request Not Reaching Child

[mdivax1!rmosher]

A process (P) generates (and can kill) child processes.  Children are
normally given a signal (kill -3) by P and kill themselves after cleaning
up and acknowledging P's request.

The problem is that (very rarely) a child process refuses to die.  No
ack is sent to P.  When in this state, even kill -9 will not kill the
child process.  However, the child process handles terminal i/o and if
the terminal is shut off and on the child can be aborted.  This makes
me think that the child is in a state where it cannot collect a software
signal, perhaps because it is in the middle of a screen write or some
terminal i/o.  Could this be the case?  What else could cause this?
Work around solutions would also be appreciated.  Note: the terminal is
set up in BLOCK mode, if that makes any difference.

Thanks in advance for any suggestions/help.