[GAMEPLAY] Rek'Sai burrow ignored Amumu's ultimate snare.

Playing Amumu in a match, I was shocked to watch the enemy Rek'Sai completely ignore the root of my ultimate. Normally I would consider the possibility that I missed her, but it was so painfully obvious as she resurfaced at the border of the ground effect of my ultimate, seemingly completely uninterrupted in her movement. There were no spell shields or allied effects in play. This was in the middle of a vicious teamfight, and I do not believe Rek'sai used her ultimate channel. I was pretty dumbfounded to ult an enemy with no results, so I'm reporting it here if it is a bug. If it is an intended gameplay mechanic, please let me know.