Aspect of Mending Stone is not applying increased duration to Earthen Bulwark. The duration should be 15 seconds with the added duration. It only lasts the base duration of 9 seconds. Killing enemies with Earth skills does appear to replenish the barrier.
[EDIT: Never mind I am an idiot. The base duration of Earthen Bulwark is 3 seconds. I had two pieces of gear equipped that had Aspect of Mending Stone which caused me to think the base duration was 9 seconds instead of 3]
As of 10th August, this is still an issue.
Unstoppable on Earthen Bulwark is 3sec (without any bonuses, all gear unequipped), with pants using Mending Stone affix (adding 6sec duration), the unstoppable activation-buff goes up to 9sec.
While standing around outside a town, the total duration of Unstoppable is highly inconsistent, ranging from 1sec to 9sec. unequipping and then re-equipping the pants resets it, so it’ll give a consistent 9sec duration, which is then reset to it’s obviously bugged state once entering a Nightmare Dungeon. doing the equipping-dance while in dungeon fixes it, until another ability activates Unstoppable (Trample, Grizzly Rage or the Wrathful Heart that proccs a 3sec Grizzly Rage).
I hadn’t noticed this issue before the 1.1.1 Patch, but that might just have been me not paying attention. It was easy enough to notice once I was running T37 Nightmare Dungeons, as the crowd-control mechanics are, already, insane at this tier.
Edit: Posted here as a reply, as there are no other ways for me, that I can find at least, to post a new thread. Hopefully someone who’s more familiar with this forum can give a hand, either by moving this to where it should be; A new thread, or by directing the Blizzard team to this post. Either way, this is getting to be a big issue for druids, as others in my clan has tested it, and saying they’ve got the same inconsistencies on this matter.