IIRC, demerphq has rewritten a substantial portion of the the regex system. If there are any bugs in it, they're likely new and different ones instead of the ones in earlier perls.
Well roughly speaking, I ripped the guts of the run-time engine into lots of little pieces and stuck them back together in such a way that it's no longer recursive and has a single unified backtrack stack, while demerphq added lots of new exciting features and fixed lots of bugs. But large chunks of the original code remain untouched by either of us and so still have any original bugs lurking within.
Dave.