Since this is only seen by some users, I think you should question them about their machine setup and usage, looking for common factors. A common version and patch level of winders or perl ^* might be a clue. Another possibility is that some users get out of your app by an abnormal route (Ctrl-Alt-Delete or the like) which bypasses a graceful shutdown.

^* Not perl, since you're shipping the interpreter in the .exe.

After Compline,
Zaxo