I've been trying to narrow this down, and it does get pretty weird. I've got it to the point of calling a closure causes the failure, and if the file lexical is read before the closure call, it doesn't disappear.

Since I can't reproduce it outside mod_perl (1.x, btw), I suspect this has little to do with typeglobs so sorry for the confusing subject.

I've got my workaround so I'm going to call it quits on reducing the code to a reproducible failure.