fact-import: failed to apply delta

I'm getting a "fatal: failed to apply delta" from fast-import. I'm using a lot of checkpoints, and I haven't had it happen without making progress, so I was eventually able to import what I was importing (bunch of stuff I can't distribute, imported from perforce with the latest version of my p4 importer that I'm still working on). Also, everything that was saved by the checkpoints was valid and correct (at least after the fact).

I'm going to see if it's reproducable, and, if so, if I can get a test case that I can distribute, but I wanted to post to see if anyone had any special debugging advice for this error message and program combination.

	-Daniel
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