Hum, I'll have to check that. Does this happen with a specific version of Perl, or in any 5.8.*?
As you mention, the problem most likely comes from XML::Parser, which was written when 5.5 was still cutting edge, and has been in "light maintenance mode" for quite some time now. That doesn't prevent me from fixing it in XML::Twig though (the length of the RT queue leaves me little hope that XML::Parser itself will be fixed anytime soon).
More generally, please, please, let me know if you find any bug in the module, I am more than happy to fix them if I can.