AHAH!

I've discovered the problem. One module was using Regexp::Fields which results in altered behavior for <cod>$&</code>, which I had not realized. Since Regexp::Fields alters the underlying regular expression engine, it appears to affect every module, even those not using it.

Unfortunately, this means that Regexp::Fields may be useless to me unless, so I'll have to find another way to implement the other part (or help the author with a patch).