Ekko cannot be knocked back during his E dash.

Is this intended? Played a game as Syndra against an E dashing Ekko and tried to knock him back during the dash and it didnt affect him at all. Didnt even seem to damage him on more than one occasion. Additionally at least once i successfully knocked him back and he teleported on top of me anyway.

If this is intended why is this the case when other similar dashes can be knocked back during the cast?