IIRC there are two problems. The first is that if you receive a signal from within a signal handler, you are likely to dump core. The second is that if Perl allocates memory within a signal handler (which it might do for a lot of reaons), you are likely to dump core. The result is that if you are using signal handlers, doing complex things in your handlers, and receiving a large number of signals, you are aperiodically going to dump core.

But note that I have heard rumor that Perl 5.8 is likely to fix this. (The problem with learning about the bugs is that they keep on going away...grumble...:-)