Screenshots Not Functioning Properly?

Not sure if anyone's noticed this before, but if you take a screenshot, either with a screenshotting program or with print screen, the cap is never of anything you're actually on. I tried tried it on a game while actively playing, and the screen grab was that of the shader compilation that runs before the game boots. If I do it again, it might be a grab from several frames in the past. I literally have to mash print screen a bunch of times in order to get a more up to date screenshot.

I haven't come across this in any native PC games or other emulators at all.