Enemies on the wrong side of Azir's wall

Sometimes, enemy champions end up on the wrong side of Azir's wall immediately after it is cast. It happens inconsistently and in a variety of circumstances. Usually, I've noticed that the enemy champion is initially knocked up and slightly back by the cast, but not pushed the full distance and so, when the wall stops moving, the enemy is on your side of it still. This happens against a single enemy champion, and against multiple champions where, occasionally, some champions end up on one side while the others end up on the wrong side. I have noticed it happen when an enemy is dashing to you (but not only in these cases), but even then the behavior is inconsistent and they may or may not end up on your side of the wall. In every case, the wall should push them back completely, or at least I think it should because they are knocked up and pushed slightly back when the wall initially hits them.