As an 'update', Parallels have now said to me:
"Since the issue requires a deeper investigation, I am passing your ticket to our next level of support who will follow up with you on your request directly."
On the Windows users thing, I suspect this is the result perhaps of a crude 'expert system' being used. This is seeing the keywords about Cortana not apparently working, and pointing out that this can be caused by the region settings, but ignoring the other problems. However it may also be slightly diagnostic.
Now I suspect the failure in the stuff like Cortana is actually being caused by the deeper fault possibly interfering with this identification. If so, it could be a clue as to what is happening.
Crossing things.
Have just updated this. Went and had a 'play' with going back to V11, using a backup I had made.
Turns out the key is that you _must_ un-install V12, before going back to V11. Problem is that a virtual machine that has been running with the problem on V12, will display the same problem when you try to boot in V11, and you can't then put the V11 tools in place to get it working. Because I'd been fiddling so much when I did it, I must have already taken the software 'off' when I did the upgrade.
This actually demonstrates rather convincingly, that it is the Parallels 'tools' that are actually the core of the problem, not the external software.
Last edited: Jan 18, 2017