So thanks to Dungeon Master's savegame we found it and solved it, and now started the process for creating an Xbox360 patch which contains all fixes to date, including this one. Once we have an ETA, we'll definitely let you know.
For the more technically inclined - the core issue (and why we never encountered it) had to do with how the game represented time. Time is stored in what is known as a floating point format and the numerical precision of the format we used tends to decrease at the time values become larger. If by the time you get to this particular scene, time was sufficiently large, calculations done on time could give wrong results that propagated through the code, and caused this particular scene to lock up. The issue was further obfuscated because only a few scenes depend on this particular time calculations, so people in quality assurance never found it because they tend to go through the game as fast as they can, and even if they had the issue, they didn't necessarily run into scenes that had this problem.
