I watched the video, and yes, you're right, this is absolutely not how it is supposed to be. Are you saying that you played all the way to Act 3 like this? Because that seems absolutely torturous.
Does this also occur if you expand the size of your hotbar? It seems very crowded sticking to the default height.
I can't help you with the bug, but since you say that you're not running any mods, I'd suggest trying Better Hotbar 2. It has some issues of its own, but it may be worth a shot to see if it resolves this specific issue.
