I bought Warlord's Tenacity level 21 and decided to test it in my guild hall. Great HP cap boost! But then I walked away and came back to find my warrior had BLED TO DEATH! It's sneaky, too, I didn't see any chat dialogue indicating anything other than he was bleeding, then fell unconscious, then died. I guess I was dumb enough to think that since buffs don't count down in the guild hall I could ignore this side effect.
The last level of this AA, Level 22, says "Beginning with rank 22, this penalty is no longer applied." Good thing. It's a big investment to acquire all 22 levels, but since the final level provides a temporary 50K+ HP boost, it's worth the effort to acquire, for sure.