Why is my robot shooting my friends?

On occasion Deathtrap will either use his blue thunderbolt or red laser eye attack on me or my friends. I thought maybe this was his "restore 30% of your shields" skill, but the attacks look identical to his normal attacks, and he'll occasionally do it to characters in Fight For Your Life.

Does he just use his normal attacks on you and they happen to heal your shield, or is this a bug or what? Does it do anything if he hits a downed character with this "attack"? How does he prioritize his target?