No one (except perhaps you) plays TW dungeons as their main content. You do your weekly, you spend couple of hours smashing an alt to max and that's it. I don't think anyone cares much about a occasional scuffed run. There's so many bugs in the actual content, fixing something like this just isn't worth the time.
Yet there is no evidence of that happening. WoW, from what we can see, is (still) doing just fine.