Windowed mode resolution not working correctly

Hello,

I have a problem regarding the resolution settings in the options.
My monitor has a 1440p resolution and it works perfectly in fullscreen,
but when I disable fullscreen it dosen't set the resolution correctly to 1440p, but instead to 1200p.

Here's a screenshot:
http://imgur.com/z8MG6KZ

Also when setting it to 1440p and then applying and pressing done it does nothing and when I then reopen the options the resolution dropdown list changed to 1200p again.
http://imgur.com/XyJvBAp

I remember it working once correctly, but I don't know how I got that.

 

Did you try maximizing the window?

 

Oh wow. Thanks.
But still, the options say the wrong thing and when I apply 1440p again it sets back to 1200p,
but I guess this works perfectly fine.
http://imgur.com/wQdKfVE