Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

I used pommel strike a while back. It spawned a dominated version of my toon, which managed to kill the spawn I was fighting, causing me to not gain any XP from it either.

So yeah . . . that was weird.

Did it spawn another toon, or just a momentary avatar shows up below your own (on the right of the screen) during the attack?

The mechanical trick that was employed in order to provide all these new melee feats is done through this "summoning/dominating," though the actual summons should remain entirely invisible on screen, as well, not steal away your toons XP.

The actual summon was entirely invisible, but managed to deliver the killing blow in a second (or maybe even third) round it was still present.