Bonds of Force

[Skinned]

Have been quadding on my wizard using SoW potions my shaman made and decided to use Bonds of Force for the first time right now. I casted it, it stuck on all four mammoths, and I nuked a couple times, and then BoF dropped on two of the mammoths, leaving the other two mammoths snared, and screwing up my kite completely.

I suppose my question is: is it common for the snare to drop off of the mobs at different times? I didn't imagine that it would do that.