I cannot say with rigor that it did work with older kernels, as prior to
upgrading to Ubuntu 12.4 I was running the non-Free fglrx drivers (forgive me
RMS for I have sinned....)

Bisecting is hard, because I am using many of the features of the newer kernel
now, and backtracking would be difficult. But if you can suggest a version to
test I can start.

I have seen other people running the Intel drivers reporting this same sort of
error (the missing busID in the drmGetBusid call), and they thought it was a
race condition (hence putting the driver into the initrd, which the Intel
driver folks said fixed their problem).