[GAMEPLAY] Karthus's corpse leaves terrain behind

Was playing ARAM when a Karthus died, and after his passive was gone, i clicked to move to where it was, but it acted like i was clicking on terrain and didn't move me. I even walked around the area instead of going straight through it. http://plays.tv/video/58dd604255891219f9/karthuss-corpse-left-terrain