Game Mechanics: Torpor Stacking Issue

[quido]

It appears that certain effects prevent torpor from landing. Tonight in a PvP happening, having Insidious Decay and Malo (not sure exactly the mechanism) on me prevented me from torporing. In a duel a few weeks ago, some necro dot prevented me from torporing myself. I asked around and supposedly this is not supposed to be the case.

I tried to replicate this behavior by debuffing myself and trying to torpor, but I was unable to with Malo and Insidious Decay (it always landed). At the time of torpor not landing on myself, I had a lot of buffs but I am pretty certain (both tonight and against the necro) that I had open slots.