Modern computers have too many emergent properties.
Gruber ran into the same problem.
The source of the bug has been located in Darwin code, the fix for now is to run Disk Utility to fix the Time Capsule store.
Of course not only should Time Machine not crash under these conditions, but it’s also really wrong for a TM crash to bring down the OS. Of course it may be that the flaw is in the OS and TM is only an innocent bystander.
Bad bug, no doubt.
The good news is that it’s well understood by Gruber-class geeks, so the fix might make it to Apple.