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It's in options, as always.

What's really annoying is that even if you set the game to "fullscreen", if your selected resolution is lower than your monitor's native resolution, if you start up the game but purposefully or accidentally click on another application before the game actually starts up, or if you purposefully hit ALT-TAB to do something else while it loads - when it loads it loads into a borderless window rather than fullscreen and it stays that way. If you then go into options you'll find that the game has disabled fullscreen mode and you have to re-enable it every single time. Alternatively if you don't change anything and exit the game completely and restart it without switching to another app, then it loads fullscreen no problem the second time. It's the only game I've ever seen with this behaviour, mind you it's a minor corner-case type of bug that will only be visible to people who run at a lower resolution than their desktop, and only then if they switch apps while the game starts.

I'm guessing this is a Windows 8 issue, because it doesn't happen in Windows 7.

Except that I am using Windows 7 Pro x64 and not Windows 8. To be clear about the problem, the monitor has a native resolution of 2560x1600, the game is currently configured to 1920x1200 "fullscreen" (not borderless). Clicking on the button to start the game up and then immediately clicking on any other running application's button on the taskbar to focus another app before the game starts results in the game opening up out of window-focus in a 1920x1200 borderless window centered on the screen, it pops up on top but does not take window focus. If the window is clicked on or the game's button on the taskbar is clicked on then the game takes focus but remains in a borderless window. Going into game options shows the game is now configured to use borderless window mode and not fullscreen as it was configured previously. Exiting the video options without changing anything (and leaving it at borderless) then exiting the game and starting it back up normally without clicking on the taskbar causes the game to start in fullscreen mode once again.

It's very clearly a bug in the game. Whether or not it is reproduceable on every computer with every video card is uncertain, but the nature of the issue is not OS-level. It's annoying but a minor issue as it doesn't cause a crash and it is something most people are unlikely to ever do. Nonetheless I've got it on my list of bugs to report to CDPR eventually.

Well that's odd then, because so am I, and I've never come across what you describe. Maybe it's an individual system thing.

Software bugs are quite often of the nature "sometimes for some people with certain conditions" rather than everyone-experiences-this-bug or nobody-ever-experiences-this-bug. I updated my post with additional information for reproducing the issue. I'm also able to reproduce it on another computer here with a native 1920x1200 display dropping the res down to 1680x1050. I frequently alt-tab out of games or click to start them and then click on my web browser or something letting the game start in the background (if I know the game wont crash/vomit that is :) so the problem hits me several times a day normally although 99.9% of people are never likely to ever experience it because it is a very non-standard thing to do plus it only happens if playing at non-native resolution with fullscreen enabled (instead of the default of borderless).

If I wait until the game code initializes the screen and actually goes fullscreen then alt-tab it works fine though, so it appears to me to be a race condition in the video subsystem init code in the game, and one that they'd probably not likely encounter because most people will use the native resolution of their monitor with borderless mode. Relatively minor issue admittedly but I have to emit a sigh every time it happens. :)

I have a similiar issue. After alt+tabbig a few times the game reverts back to borderless window which cut the frames in half. And almost never the game starts in full screen. 99% its in borderless and i have to set it every time..

Change it in the config file the save way you described in the other topic, then make the file read-only.

That never worked....

I just pressed play and i let the game fully load before i touch anything else like the guy above me stated. It worked fine.