It's a problem with the game and another mod triggering it, look earlier in the log where it failed to unload, that's the one causing it.

The primary problem is Keen refusing to crash the game on errors during unload, causing all sorts of NEW bugs that normally don't happen, like this one. But this is IMO a good error because it prevents other sneakier bugs from happening during the world itself... you and mod authors would be sent on wild goose chases for errors that never happen normally.

Can you also post the log, I want to replicate this and see if I can detect it and do a proper error and a forced game crash to fix the leakage.