openmw.org

Same issue. This isn't really "solved", at least since 0.47.0 RC7.

Basically clone displays are unusable. No matter what resolution you have your desktop in or what you set OpenMW to (either the launcher or in-game), OpenMW always reverts to 1280x720 (why? odd choice). You basically have to die with single display. The change it's made more annoying because of shitty Intel drivers that reset the refresh rate on every clone<->single display transition. Set to single, change 59p to 60p, play OpenMW, set to clone, change one display from 59p and the other from 29p to both 60p. Damn.

Weird bug though. I've used clone displays since forever and never had any issues with games. Any idea what could fix this for good?

If it only happens with cloned displays, then I'd be inclined to blame the shitty Intel drivers or SDL (or possibly how we're using SDL).

In the launcher go the "Graphics" tab at the top, then across from "Resolution:" It should show some thing like this:
O standard: 1920 x 1080 (wide 16:9)
O custom : 1000 x 750
Custom is selected, oddly, which is the resolution you will see when the game is launched, just change the custom resolution to the native resolution or choose the preset one from "Standard:"

I have tested it & is works