In the Learn tab, currently there's an area below the lowest-positioned heroes in each group of hero icons where it still pops up the tooltip for a hero. Additionally, hovering over a small part below this area makes the selection cursor start to freak out and flicker.

For example, hovering over Sniper's icon will make the tooltip for his name pop up; hovering the cursor just below his icon also shows his tooltip; lastly by slowly moving the cursor farther down you'll find a region where the selection highlight (and usually the tooltip) start flickering.

(Tested in 1280x1024 windowed mode, with vsync off)