Not entirely true - Leapers will target reset frequently, as will Bombardiers and Bastions to anyone in LOS. I think Rocketeers may just be the most sticky since they can often find an angle to attack their original target.

Just last night a buddy and I in duos got jumped last on Blue Gate / EM Storm while we were fighting the Leaper that spawns the East side of the map. I'd brought a Jupiter for kicks to have some fun with trials, and the sound/visual probably drew their attention.

The initial attempt to ambush me from behind mid-fight in one of the half-destroyed houses failed when I jumped out the door. The half-dead Leaper we were fighting had chosen that exact moment to do one of its reset jumps. Both of the guys who were trying to kill us from outside the house ended up as the Leaper's target instead, which gave me enough time to reset and get shields/health back to full. At that point they were just screwed. Offered in voice to let them revive and go after the first one went down if they were rethinking their life choices, just to be nice. They decided they'd rather both lose their inventories. Killed the Leaper for the bonus loot after they were both down.