Thanks for the error report, I'll dig into it and figure out what's going on. Someone in the Discord was also talking about it and I think something goofy might be happening with it. I might have used an older version of my test code for it instead of the tested one I had ready. I gotta look at it to be sure.
Do you happen to know which version of RenPy this was in? I doubt it's an issue with RenPy, but it helps me reproduce it.