pretty sure this is a known bug. I think it has to do with the boss firing up any toggles or click defense powers they have before you get to them, thereby interrupting their animation. I haven't played around with it too much, but try modifying the boss's powers so they only have attack powers (if possible) and see if that does it. Someone else mentioned it could be because of auras. But either way, I'm pretty sure the devs know about it. Unfortunately, unless it's easy to fix it doesn't seem like the kind of thing that would get really high priority from them.
bababadalgharaghtakamminarronnkonnbronntonner-
ronntuonnthunntrovarrhounawnskawntoohoohoordenenth ur-
nuk!
After careful planning and preparation, I have finally started my MA storyline... only to find out that I cannot make my Custom Boss perform his opening emote or say what he should say at certain levels of hit point damage. Every time I reach my Custom Boss, they always appear in a badly looped taunt.
Has anybody else encountered this? Is this a known bug? Is there a fix? Or am I just stoopid?