Is the Display at the end of the Thunderbolt chain? It should be TB port on Mac to drive to Display. I've two TB drives hooked up in that manner -> TB port to drive 1, TB port out to drive 2, TB port out to Display. No problems.
If the Buffalo drive only comes with one TB port, of course, that could be a problem...
I figured that I got a deffective Buffalo 1TB thunderbolt unit. The funny thing is that this deffective hard drive caused the display to turn off. I have read in several reviews that the cable used by Buffalo has some problems, I wonder if it had a short circuit or something similar.
I bought a 3TB Lacie drive thunderbolt compatible and it is running fine.