I'm using 5.8.0. I'm looking to try on a newer version.

That's probably the way to go.  5.8.0 definitely had a few bugs — you might have rediscovered one of those :)

It looks like it's trying to free memory at the wrong address. OTOH, as this happens after a call to getc in libc, it could also indicate a libc-internal problem...

P.S.: there's no guarantee that $SIG{SEGV} will work, because when a Perl program gets a SIGSEGV, the interpreter could already be in an inconsistent state (memory messed up, etc.), so it might no longer be able to run any signal handler code.