Hello,
I’m helping out on trying to reproduce the issue you’re seeing.
As far as the black rectangle / freeze goes, I’ve only gotten it to happen once. The tab being dragged out from clicking quickly and then moving the mouse doesn’t seem like a bug however. As you mentioned with your slower mouse. I’ve been able to get this to happen with Google Chrome and Microsoft Explorer as well however. It seems like an issue of the mouse registering the click and movement as a click and drag due to it being so quick that the program, when in a laggy state, registers them as one action and counts it as a drag, as you mentioned.