Kernel panic -- Memory modified after free

I upgraded my kernel yesterday, after testing alc_at_'s patch for mmu_oea
(PowerPC 32-bit, AIM), and now I'm seeing the kernel panic in the subject.
Unfortunately, I didn't keep my knonw-good working kernel from prior to
testing alc_at_'s patch, so the most recent kernel I have that works is from
over a year ago, so booting to it means I get no networking, as the ABI has
changed.

With this, every time it panics, it shows "Most recently used by 'bus'".

Has anyone else seen this kind panic from recent kernels?

For further testing, I tried downloading the kernel tarball from allbsd.org,
from the 20120601 snapshot, and that also shows the same panic.  Also, this
only occurs on my G4 tower, which is a dual processor machine.  The exact
same kernels work fine on my PowerBook, which is single processor.

- Justin