I upgraded Win 10 to Version 1607, OS Build 145393.10 yesterday night and -- surprise, surprise, surprise -- subject problem went away!
Unfortunately, I cannot provide detailed information about the root cause of the problem and yet suspect a bug in the previous OS build that sidelined/disabled the ‘Backup and Restore (Windows 7)’ functionality.

I can back-up to my NAS again, burned a new repair disk and created a new system image. I also can sleep better now and recommend upgrading Win 10 to the aforementioned OS Build when you experience subject problem(s).

In conclusion, I am not a software developer. I am not into OS hacking. I am merely a retired engineer owning and operating a high-performance dual CPU workstation (Dell Precision T7910). So, the windows OS and task specific apps are tools, in my perspective. Very important tools! Moreover, I cannot afford loosing valuable programs, data, graphics and information, because of data backup and restore anomalies...

And since my problem is that I have thoughts, a clean install on every OS glitch and starting all over again will never enchant me. On the other hand -- contrasting Apple’s UNIX based open system -- Windows 10 is an exclusive book with seven seals into which I have only a limited view. So, I trust the programming talent of Microsoft software engineers and hope that the new Win 10 release will now have the same robustness I have become accustomed to during the Windows 7 years.