resonant evil

So twice today I've been using Rusty Painwheel against a Resonant Evil, and I tried to throw him when he had zero stacks armor, only to end up stunned before the throw even completed, which doesn't seem right. If I haven't thrown him yet, he hasn't been hit, so he shouldn't have a stack of...

When I fight RE BB, two things happen: BB stops taking damage at 3 stacks of armor instead of 4; Stun procs without any visible armor buffs (actually lost a streak to this). Both of these things point to the fact that one of the stacks isn’t shown. I don’t see such an ability in RE’s skill...