Nautilus passive on Vayne

Yesterday I played a game as Nautilus support against the opposing Vayne. I engaged on her with my Q (Dredge Line), wich hit, and after that I wanted to Auto Attack her to trigger my passive (Staggering Blow). The Auto Attack went off and Vayne took damage, but wasn't rooted. This seemed to be caused by the use of her Q (Tumble), but if I recall correctly, that shouldn't happen. During the rest of the game this bug kept occuring. Vayne still could be snared when she didn't Tumble, but as soon as she used Tumble when snared by Nautilus' passive, the snare wouldn't happen. As an example you could watch the replay replay.gg has provided me with to see the bug for yourself. The link to the set-up for this link is available in the link option in this form. Lastly I think I should mention I was using the AstroNautilus skin, while I haven't tried the bug with the Classic Skin.