Weird that they didn't say anything about it? Wonder if someone just *forgot* lol.
There was just a miscommunication about when this was going live, but it's been added to the PC Live patch notes now. Apologies for the mix up here. For visibility, here is the full change to this item set:
[*] Hrothgar's Chill:[list]
[*] This item set now deals 13% of the added Physical and Spell Resistance on the initial target, down from 26%.
[*] This set now ignores mitigation on all targets to ensure it remains a potent tank punishing set.
[*] Fixed an issue where the explosion damage of this set was not being affected by Battle Spirit.