The window of Factorio (on Windows) has a slight issue that it shows a 1 or 2 pixel border around the window. When it's maximized, it's easily noticeable compared to other applications that run maximized.
Following what I read on reddit, I've tried it myself as well.
Basically, Factorio has the extended window style WS_EX_CLIENTEDGE enabled. According to the Microsoft MSDN this causes the window to have a sunken edge. When this style is removed from the window, the issue is solved.
Please take a look at the screenshot examples.
I'm not sure if you guys call this a bug, but I'm sometimes annoyed by that white border around a maximized window. It would be nice if you can resolve this natively.
[Harkonnen] [0.15.18] Sunken window border style on Windows
Re: [Harkonnen] [0.15.18] Sunken window border style on Windows
Thanks for report and quick hint on styles Fixed for 0.15.22