I'd interpret Warding Bond's effect to be comprised of 2 components:
- the Ward: +1 AC and resistance to damage
- the Bond: cleric takes all damage the bonded target takes

I don't think Transfuse Health deals damage to the caster, but rather has Health as a resource cost for casting the ability. I can see why it would bypass the "Warding" component, but I do agree it is questionable whether the "Bond" should share the HP removal effect or not...