Installed 22
Backed up in PR 1.2
Killed the device
Restored to 1.2 >> success

Installed 22
Backed up in 1.2
Upgraded to 1.3
Restored to 1.2 >> success (see above warning in bold)

Installed 22
Upgraded to PR1.3
Installed 22 again (*)
Backed up 1.3 using 20101022
Killed the device again
Restored to 1.3.

That means, basically, that version 22 is solid whatever way you go, provided that you (*)reinstall it after OTA. I can't swear it won't work after OTA, but I did reinstall it to be on the safe side, so all my tests are with a reinstall after OTA.

(*)By reinstall I mean followed the instructions in first post. Since I already had backup menu and a working OS, I just went to the tar command to overwrite the files (and the the rest of the commands).

By now I have a BM.sh that does it, in /media/mmc1/Ndi/MB.sh. Along with other scripts I'm tired of running, along with a backup of repository definitions and a few other files. I just wished the flasher image came with rootsh installed. When recovering from a failed restore, I flash, followed by rootsh, followed by an "sh /media/mmc1/Ndi/BM.sh" and a restore.

I'm down to 2 minutes.