When I read-back from the failed /dev/hda5 partition on my PC, it is not corrupted, and the contents match what should be there. So.. why no workie???
Very confusing. File-by-file comparison between what got written to hda5, and what should have been written: no differences (but there are differences in the binary contents of the partition, weirdly enough).
But if I then manually "pump" hda5 onto the drive from my PC, without changing anything else, the builder then works when re-inserted onto the empeg. Screwy. This is with the exact same binary image that is normally part of the .upgrade file.