From your post it is not clear what is from the child and what from the parent. Could you just launch the server program with strace and the -f flag so that the PID appears on the output?

Anyway, it looks to me that the cached $$ bug is affecting you. DESTROY is being called on the child process but $$ returns the parent PID.

Something that is clear is that the process receives a SIGTERM while on the middle of the DESTROY call. That explains why an END DESTROY is missing.