Poppy with Mercury Treads Stops Dark Binding

I was playing a Ranked game as Poppy Jungle against a Morgana Support. I got Merc Treads with the idea of reducing the snare time of Dark Binding to avoid getting picked. However, after buying the item I was no longer being snared by the ability. This occurred around 3-4 times after getting the Tier 2 boots. This happened at least twice while the enemy team was sieging the Mid Inhib turret. As well as being noticed once in a team fight by the Inner Mid turret. The ability still dealt damage, which was accurate based off my Magic Resist, however it would not snare me. And again I was playing Poppy.