It always has been this way, at least since i’m playing this game ~2,5year. Sunbird always resurrected weaker, than original copy. Only after getting that +X magic, he starts to ressurect on same level.
I know. So the title: “old bug”. The same problem was true for the all transformations. But the transformations was fixed some time ago, and when I checked the Sunbird, it seemed the fixed too, so I let it go. Until discovered at Arena that Sunbird still affected by this. Seems, it’s the only self-transformed troop that works that way.
I’ve passed this on.