I finally upgraded to High Seas and went to fight Corgul. I imbued a longsword with Repond Slayer and had at him but I was doing normal damage with armor ignore. I tested the weapon on other repond vulnerable mobs and it was doing double damage. I know Corgul has high resists hence using armor ignore. Other folks on the warrior forum have denied experiencing the same problem so there seems to be some weirdness going on. This was in Trammel on Napa Valley about two weeks ago.