I don't know if I missed the answer as it is submerged with other facts.
A backup image is just that. An image you should be able to restore/flash by either USB or Image Manager. Concentrating on what it does now and ignoring what it should do prevents a fix/improvement.
Just to re-iterate. In openvix, Image manager invokes ofgwrite. As with previous image manager/ofgwrite issues/problems, first step is identifying:
Is issue image manager?
Is issue ofgwrite?
Is issue both?
So back to a basic question (hopefully we will get a simple answer). On other images, can you flash a backed up image using ofgwrite?