There's something like this in every desktop Linux I've tried, which made it feel like using the mouse was in some way weird and broken. But I've been using it for long enough now that it either got fixed, or more likely, I got used to it. I don't even remember what it was, something about clicking drop down menus a certain way?

Reminds me of the first time I ever used classic Macintosh System OS, and how you have to hold the mouse button down to keep menus open. It doesn't take much to throw everything off.