Status Update 1: I have tested the fail on Strawberry perl 5.18, 5.20, and 5.22 on the failing windows machine and they all failed. Weirdly this is the only perl script failing in this way on that machine. I tried the failing script on a different windows machine and it passes. After working on reduction of complexity in the background modules the failure still occurs but has migrated to an earlier point in the script. (Although still failing at the $self->_DESTROY command when traced in the debugger) I suspect some weird corner case interaction between Strawberry perl and windows but since another windows box passes I'm now pursuing this as a pure windows problem. I just wish I was able to narrow it down enough to write a bug case for submission somewhere.