I believe this has been reported before, though I can’t be certain or find the topic; so I’ll post it anyway;
After mining for a ‘certain amount of time’ the experience numbers begin to overlap, and the blue bar extends to the end of the screen. It’s not at all game breaking, and only really applies people with far too much free time on their hands, but I figured it was something you’d want to be aware of non-the-less. Here’s a screenshot;
I figure most of these ‘issues’ will go away with all the new UI updates, but no harm in bringing them to your attention.