I have a theory about what's going on with heals causing damage during Raid battles. It could be that only 1 heal effect is allowed per turn, and that subsequent heals are actually OVERWRITING the effect of prior heals. Thus when you get a heal from another party's Andromeda, then heal yourself, if your heal is less than that of Andromeda's then it actually reduces your party's HP. Unconfirmed, but it explains what I just observed with my team.