As far as I know, it looks like im keeping my threat after knockbacks. I realized it when I was tanking Dire Maul and the trash mobs that did knockbacks no longer felt like a pain in the ass to tank and my KTM saying its all good. I'll be tanking MC today (8/27/17) and can further confirm if the bug has been fixed when I tank Giants, etc.
Update: Still losing a shit ton of threat on knockback from MC giants.