Hammer of Gods Weapon Swap

When playing Druid it is not possible to swap to "Hammer of Gods" and back to a bear. The Hammer of Gods DMG will not be applied, but fissures will trigger.

I thought it is weaponset releated, but this doesn's seem to be the case(tried to only apply "Hammer of Gods" to the hammer weaponset)

Then I tried to stay in human form for the animation time of the hammer and the dmg impact. Sometimes the hammer does dmg in this situation and sometimes not.