I guess it's the MG_TYPE='r' line which is indicating it's a magical Regexp, and the magic isn't affected when it's bless'ed.

A quick look through my copy of perlguts however reveals that.. err.. r isn't listed as a possible value of MG_TYPE.

Now planning on hitting Inline::CPP a bit more when I get home see if I can magically regexp'ify strings and visa-versa..