I've got 12 of the basic researchers in the same basement of a qeynos 7 room house (mixture of races) and all of them always show the bar for their 'master' on mouse over. My husband has similar in the freeport mage tower prestige house and some of the progress bars on his apprentices don't show all the time.
I've got my heroic and raid apprentices in a different house from my regular ones, he's got his in the same house. I wonder if there is some interaction in having two (or more) apprentices belonging to the same toon in the same house?