Hi @shingen,
Oh, I see what you mean. Thank you for the video 
Yeah, that’s a bug that we’re aware of and are working on which was originally reported here: WIP: Unable to delete all classes. Currently, you can’t delete all classes (which can be annoying, especially as it’s easier to do so with the global class manager now).
I updated the ticket with your report but I’ll close this thread just so we can have one thread to follow the bug.