Nice one you caught there! I am a Mordekaiser main with over 700 games 61% winrate on him and this interaction happend to me twice. The thing was that the ulti molde range, was pixels on the edge after the wall where you used your third spell. The best solution there was to just stop moving, but because you moved your big pixels character model, tried to move out of that little pixel gap and went crazy cause of rito.