What you were expecting to happen, and what actually happened
Because of the ordering of the words in the text (pull, then damage), the targeted troop should be pulled to first position (moving top troop down) and then should die. Instead, the troop is killed first, and then nobody moves.
How often does this happen? When did it begin happening?
Always upon lethal damage
Steps to make it happen again
Target an opposing troop with Chief Stronghorn’s ability when the ability would do lethal damage.
True. And Emperor Khorvash would drain before stunning, until they changed it when Champion of Anu came out with the same wording but different effect and people noticed it (in conjunction with the new ancestry and mana shield traits). So they “corrected” him after it was reported.
It also makes a difference if you’re relying on spells that deal damage based on a troop’s position, such as Charm, or any spell effect that says “adjacent troops”.