In reply to my earlier post regarding assigning loot via roll, I suspect it's because I have the other toons passing on random loot. Given all the other bugs I've encountered, seeing one where toons having elected to pass still get a roll prompt wouldn't surprise me...

.. and on that note, I've run across another bug I thought I'd share. When using master looter, if the master looter finds a bit of loot and does not IMMEDIATELY assign it, that loot can be lost. If the loot window is closed, the corpses will turn non-lootable. If, however, another mob is killed within the vicinity of the original lootable corpse, the item will show up again for looting. Yay. So, be careful when using master looter.