It's completely changed on the PTR for 7.1 now too. On the PTR currently UA actually each has its own spell icon debuff on the target and you can cast it up to 5 times on something (so shows 5 separate UAs on them each with its own timer) Originally they were having it show a stacking number from 1 to 5 but that just got changed, for whatever reason, but they must have been having issues with it because Rot and Decay was not refreshing UA before. The other good thing about the 5 separate UA icons is that each one buffs your shadow bite damage from your fel hunter by 50% each, so you get 7 buffs to shadow bite damage from corruption, Agony and 5 UAs.
Now on the PTR Rot and Decay is refreshing the duration of UA and you can let it drop all the way down to 1 second left and when you refresh it with Rot and Decay it still does 100% of its original damage per tick. It also feels like Rot and Decay is adding 3 seconds per drain lift tick as opposed to 2 seconds like it was on live, it feels much easier to keep UA's refreshed to full duration now on the PTR.
I can see you being able to possibly UA stack two targets and keep them up now with the way UA and Rot and Decay is working on the ptr since you wont lose any damage anymore on your stacks if you are a bit slow on refreshing them (unless you let them completely drop off). You have to work around people dispelling your stacks which will be less punishing for them to do now since they are lowering the backlash damage for dispelling them, but think that if you constantly keep stacking two targets that it will make it much harder for them to keep up.
Edited by Drizzilx, 10 October 2016 - 09:20 PM.