The paladin Blunted Blade disc is being knocked off before its allowed to run the full duration. This issue started occurring around RoS release. The disc has had similar problems in the past but fixed to be stable in EoK. There appears to be multiple things now which can cause the disc to be dropped. Sometimes the disc is dropped very quickly, other times it will stay up for a min. With just a guess, i would have to say the issue is with the min damage modifier.