I didn't report this to rt.cpan.org because they were all discussed on the Alzabo mailing list with discussion and Dave was already there.
Nice guy by the way. You should stop by the Minneapolis perl monger meeting sometime if you ever find yourself here at the right time.
I don't remember the specific problem in question, but now that Params::Validate uses XS internally, I'm not surprised if it occasionally produces weird errors. That said, I use it in production code all the time, and it's very widely used as a result of being required by Mason, and I don't get a lot of bug reports.