https://bugzilla.kernel.org/show_bug.cgi?id=54381
--- Comment #3 from Alex Deucher alexdeucher@gmail.com 2013-02-24 23:14:49 --- (In reply to comment #2)
That explains why the 3 monitor setup works, but 2 monitors plus a projector don't: two of the monitors are the same. Interestingly enough, it works completely fine for any kernel < 3.7.0. I have been using this setup since at least a year or so and never had any problems with 3 different display units (until 3.7.0). Considering what you said that confuses me, since it shouldn't have worked as problem-free as it did, should it?
It probably worked by accident previously. Presumably the pixel clocks on the two monitors that were sharing a PLL were close enough that the monitors were ok with it. What modes are you running on the two monitors and projector?