SOLUTION IN MY CASE
Simple: executed the included in Windows disk repair option. Right click on problem partition --- one of the tabs, restart as instructed, Windows repair utillity starts during reboot.
Installed bootmanager that made a dedicated partition. All didn't work due to known or probable factor I don't mention here.
Looked on forums. No explicit solution found. Program tree size free edition mentioned on forums several times showed the correct disk usage. Had the idea: its a partition fault.