The invulnerability of the Heorot’s Protection node of the Fury Leap tree only applies to Health and not Ward.
I am sure this is a bug, because the Invulnerability from the Juggernaut tree in Warcry does apply to Ward.
This issue also affects Maul when inheriting Fury Leap’s skill tree in Werebear form.
Tested by standing in the fire pit in Soulfire Bastion and using the ability inside it.
Video:
