Huge Popup Window

It only happened to me once, on Summoner's Rift, and I have absolutely no idea what happened there. I tower dove an enemy on mid or bot at their last lane tower, closest to their base, moving my cursor to the top left corner to to head around the tower and back into the jungle, when suddenly 2 huge, illegible windows pop up in the middle of the map, blocking my mouse clicks, rendering me unable to move that direction. They looked like hover-over tool-tip popups!