I tried other versions of driver - and even 15.12 is turning on DITHERING - but just on LP140WF screen!
So for at least 4 months there is no progress with this issue
I even tried EDID driver from ENTECH to `force` the EDID of LP140WF screen to NV140FHM screen, but the dithering is still disabled
So it is probably not switched according the EDID....
After I read the Lenovo forum I've changed my display with a full hd one but the problem is still there. To be honest, there is a small diference but just not enough.
I went to the service and they just replaced the mainboard, but that didn't produce any changes.