Interesting problem... You've already checked globals, you say, so Devel::FindGlobals won't help.

I guess you've already put some print statements in the DESTROY routines, which is how you know when they're being cleared up?

If that's the case, then I'd suggest printing out the call stack and $self when you construct all the objects of that class, and then print out $self in DESTROY and compare to find out when the "guilty" references are created.

As an alternative, you could add a copy of the caller results from the constructor to your object, and then print it out in DESTROY to cut down on the noise.

That should help you track down the issue, I hope. I know you were looking for a module, but I hope this does the trick.