Umm, possible bad news. In 2012 I believe AD changed something in the way it asks for data and when I try to tumble or interact in IPR with Progressive or iRay, it crashes or halts.
They aren’t using (or ever have been really) the correct API. So that’s just my current experience. (Also make sure your framebuffer settings aren’t set to cache)
Bunkspeed however, does this correctly.
I have no idea why AD has dropped the ball, sat on it, crushed, ran over, and set fire to mental ray integration. 
(However, product differentiation could mean you should buy both Maya and Max. . .ugh. Greedy.)

