This is more than likely related to the issue I described in another thread:
When the bird revives, it appears to set its level to what it revived at (which is based on magic, since it basically summons itself) which then persists after battle. This appears to be an issue with the way the data for troops is stored client side, as entering a game will revert the bird to its correct level for that battle. Restarting the game also fixes. If you have already leveled the troop, you should just be able to ignore the problem for now since it should be the correct level in battles.
It may not be intended that Sunbird’s magic is affecting the level it respawns at in the first place, since it has very low magic base magic for this purpose. Logically, it should respawn at current level in your collection, regardless of magic, like trait summons. Fixing this would probably fix the other issue as well.