I plugged my Cintiq 13HD in and it is also at 1920 x 1080, no issues here.
Photoshop runs fine at the right resolution on both my main monitors, but when I drag Photoshop over to my Cintiq 13HD it puts it at the wrong resolution (Photoshop itself is blurry, yet the Cintiq background is still at the right resolution).
I am running Windows 10 and this is the first time I have tried it on Windows 10. I know it works perfectly fine on Windows 7 and Mac OSX
Photoshop is coded not to use Windows scaling. Did you modify tot Windows 10 register to uses external manifest files snd create one for Photoshop. Windows sealing is per display. Make sure your Cintiq display is set to Windows scaling to 100% not any other windows setting.