Oh I had a similar bug but with defaulted dicts. Default args are constructed once and reused. Not a problem for immutable args, but mutables like dicts (and sets I’d also assume) are all shared.
EDIT: whoops, didn’t see you spoilered the answer, my bad! If it helps, i found my bug when dealing with cross-thread stuff, so that was a fun moment to bisect
Ah sorry I meant a default argument which was a dict, thanks for the tip tho!