Hello!
My apologies, this sounds like a bug which is fixed in the current steam release but isn't fixed in the mac version here. I don't own a mac myself so I just haven't been able to playtest the latest update on mac yet, but a fix will be coming.
In the mean time I'm afraid the only fix would be to delete your persistent data file. On mac I think you can find it under ~/Library/RenPy/.
Hope that helps, sorry I couldn't be more helpful!