There was some revisions on $SIG{CHLD} = 'IGNORE' that went into Perl 5.8.1, I believe. The short of it was that on some operating systems prior to 5.8.1, doing a SIG{CHLD} = 'IGNORE' could cause Perl to wait() for the forked child process twice and cause an infinite hang.
If you are using something prior to 5.8.1, you might be seeing another symptom of the same problem. If you are using post-5.8.1, it could be that the patch broke something else.
If you are the most recent version of Perl, it sounds like something you might want to submit a perlbug for. When you do, you might want to refer to bug #
18849
