erisuser: Thanks for your input. Helpful explanation. It still baffles me then, what could be screwing up my backups. And this problem just started a few weeks ago, and only, it seems, with my nandroid backups.
I did download ScaryAlien's newer AFV, which by the way has a nicer look & feel to it. So I'm going to peak around some files, create a new backup and then go inside it and look around.
Per your explanation it sounds relatively easy so I'm off to search.