Morde's ult is a little weird...mechanically

I'm not ranting about his ult's power but as the victim of his ult sometimes when I'm trying to flee and get to the wall my character will stop moving altogether unless I go the exact opposite direction. I understand the wall is there to stop fleeing players and that's fine but if I'm against the wall and try to click to right or left of me my champ won't move. Like at all. I'm not sure if I'm imagining it (or I'm just dumb and it's stunning me but I don't think it does that should though) or just keep mis-clicking somehow but it's kinda annoying for the shadow wall to stop me from moving anywhere where Morde isn't. And whenever I click outside the wall my champ doesn't move at all even when they're in the middle of the ring.