I'm in the process of changing the ratings on a large number of films
Don't do that now with the current version of Coollector. Indeed, the next version will have an improved rating system. What's changed is that it'll be possible to refine your rating with a plus or a minus modifier. For example, if you rate a movie as "good", but you hesitated to rate it "very good", now you can rate it "good+".
I have finished implementing this feature, and I can give you the new program if you're interested.
If I click on a rating button, then quickly tap e.g. the down arrow, then again quickly click on the rating button
I've been able to reproduce the bug, thank you very much for your feedback!