You can't use lightning armor first round to prevent debuffs anymore, the change to it makes it remove debuffs (which doesn't seem to work, as the ignite and poison stacks remained after activation) instead of making you immune. Once you are under chaos, acupuncture, etc, you don't have the ability to activate lightning armor.
You never could cancel debuffs with Light Armor, but it makes you immune to them after you cast it. As far as i know it didn't change at all, they just changed text.