I found a few bugs in OpenGL.xs in Debian's sdlperl 1.20.3-1 release.
I've patched the ones I can't work around, and sent the bug report and
patch to the Debian BTS. In a separate mail exchange, chromatic asked
me to send the bug/patch link to this list (which I've just subscribed
to, so replies to the list will reach me). So here you go:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=275769
I don't know if the patch will apply to any of the upstream branches,
but it shouldn't be too hard to apply by hand if necessary.
-'f