So.. after some thought, I have a sneaking suspicion this only happens if you have your loot type set to something other than your default. My Medicine spec Operative didn't have any problems with this until I was over Renown 100, which is also the time I decided to set my spec to get Lethality loot, and it started happening. My tank I just got up there, is set to default and she has no problem. Though I've found the way to avoid it coming up empty is to make sure you clear the stash every time you open a box. But I'm going to test this with my Operative by putting her back on default spec and seeing if she still has it.