I'm trying to run the game in windowed 1440p resolution, but it keeps setting it back to 4k and fullscreen every time I restart it (I have GeForce 1080). All other settings seem to be saving correctly.

Is there a resolution to this?

I have found the configuration file, and it appears the game is not respecting those settings, because they are correct here:

<?xml version="1.0" encoding="utf-8"?>
<PublicSettingsFile>
<GammaInitialized>true</GammaInitialized>
<Volume>0.5999999</Volume>
<SoundVolume>0.5999999</SoundVolume>
<AmbientVolume>1</AmbientVolume>
<SavedLanguage>ENGLISH</SavedLanguage>
<IsCrouchToggleable>false</IsCrouchToggleable>
<ShowSubtitles>true</ShowSubtitles>
<VSyncMode>EveryVBlank</VSyncMode>
<UseFullscreen>false</UseFullscreen>
<ScreenWidth>2560</ScreenWidth>
<ScreenHeight>1440</ScreenHeight>
<RefreshRate>59</RefreshRate>
<Headbobbing>false</Headbobbing>
<Crosshair>true</Crosshair>
<Fov>55</Fov>
<ChangelogVersion>0</ChangelogVersion>
<CurrentQualityProperties>
<SelectedAntialiasing>SMAA</SelectedAntialiasing>
<SelectedSSAO>HBAO</SelectedSSAO>
<SelectedChromaticFlares>On</SelectedChromaticFlares>
<SelectedAnisotropicFiltering>Enable</SelectedAnisotropicFiltering>
<SelectedTextures>High</SelectedTextures>
<SelectedShadows>High</SelectedShadows>
<UseChromaticAberation>true</UseChromaticAberation>
<UseMirrors>true</UseMirrors>
</CurrentQualityProperties>
<GameQuality>High</GameQuality>
<Gamma>2.19024849</Gamma>
</PublicSettingsFile>