If you cast steal on a target while in the animation for flanking strike, your steal will teleport you to target but it will not damage them even if traited. Instead, it will show out of range.
Also the tooltips for the healing gained by grandmaster trait “assassin’s reward” are wrong in the case of flanking strike and larcenous strike due to the initiative shift. Also just confirmed that you gain the wrong amount of HP for these skills too.