I have a solution!!!
before looking on the net, I decided to uninstall the monitor driver (and at the same time check the option to delete it in the driver cache on the system - so it didn't come back, so to speak) and rebooted - the monitor is now classed as a 'Generic Monitor' in the advanced display properties - and the problem is solved!
hope this works for you
all best,
B
UPDATE: I noticed today that Windows Update tried to install an 'update' of the self-same monitor driver in question - so I suggest setting Windows Update to notify before installing, just for the time being, until M$ sort out a *correct* driver for this monitor... talk about 'Anti-Update'...