This nerf has always been unasked for and mostly unwanted by crats of all levels - Cz has even admitted that they've nerfed it much more than it was supposed to be -
Had a chat with the monster designer, and apparently the "immunity" flag got attached to a lot more monsters than it was supposed to. So it's not intentional, but don't expect it to be reason for an emergency patch. My current impression is that it'll most likely be in the next regular patch.
Next patch? Thats a long time with massively reduced skills. Many good threads on the crat forum if you have any interest.