I just completed a random heroic oculus, but didn't get any gems. Only one person in our party got the bag, and everyone else had an empty chest.
Here's what happened:
- Our first tank left at the start of the dungeon
- We used the dungeon tool to find a replacement
- The replacement tank was the only person to get the bag
So, perhaps looking for replacements disqualified us from the extra loot? If true, this is clearly not "working as intended," since it punishes people for staying in the instance. The only way you would get gems is if no one quits, or if you go ahead and four-man the rest of the dungeon.
Edit: Someone below said they were able to get loot even after finding replacements... sooo... I dunno? Either way, my group got nada.