Blizzard disables 'anti-exploit' experience cap mechanic
For a while now people have been complaining about a new system that caused experience gained by repeatedly killing the same mobs as they respawned to be reduced, saying it was too punitive. Now Ion "Watcher" Hazzikostas has posted explaining that the mechanic, intended to combat exploits common to power leveling, has been disabled.
That said, clearly this implementation is far too strict, and is triggering from a wide variety of normal activity. We're going to disable the functionality entirely and look into a much more narrowly targeted approach if and when we reintroduce it. Apologies for the inconvenience and the lack of response on the issue - we were working on understanding exactly where the algorithm was going awry, and now that we've done so, we'll be taking action in the near future.
So if you happen to enjoy grinding and don't mind it being somewhat less rewarding, while not wanting it to be almost completely so, this change should please you. Still, there probably should be a mechanic for combating power leveling abuses involving tagging mobs and then having a whole party or raid backing you up to kill what you tag, and I hope that when they do come up with an idea for it, it's a little less broadly implemented than this was.