This is starting to sound repetitive, isn't it. Ah well - if I'd been keeping a Perl journal a few months ago, every entry would have been about B::Deparse :-)
Graham Barr pointed out that there's a flag you can set which instructs eval to catch its own errors, so that you don't have to. So I've changed A::FP to use that, instead. And I've uploaded it to the CPAN. I'm a bit nervous that I still haven't managed to get in touch with Matt Day: if you know how to get hold of him, please let me know.