I'm using Gentoo Linux on my Dell Latitude E6530 laptop. It has a nVidia GF108GLM video card and it provides the Optimus technology, which I have disabled in the BIOS in favour of using only the nVidia card. I'm using Gentoo kernel 4.9.34 with its nouveau driver, mode setting active with no related, specific kernel argument.
I noticed a strange behaviour when I have applications viewed full-screen. I haven't been able to determine a pattern with 100% certainty but in 90% cases it happens when I have a web browser active, either full-screen, reduced or in a normal window.
What happens is, after a delay that is mainly random, I see my entire screen suddenly overlayed with a full-screen image that covers the entire screen, completely overlaying the visual of the application I'm currently using. For instance, say I'm working in a full-screen terminal or in a full-screen Geany. Then all of a sudden the entire screen is covered with an overlay image of what happened to be visible before on my screen: it can be a render of what the screensaver was showing right before I unlocked it or my desktop background picture.
In certain cases I can move the mouse pointer over certain areas to see the application I'm using coming back partly in areas the mouse is hovering. Sometimes the only way to see what I'm typing is to switch to another application window (Alt + Tab) and back but the "rogue" overlay image always comes back after 2-3 seconds.
The phenomenon can take some random time before it manifests itself. But when it happens, it takes only 2-3 seconds to happen again when I switch to another window and back.
The glitch happens (like 98% of the time) when I'm using an application that is displayed full-screen and I have a web browser active, full-screen or not. But it also happened, just once while I was using a non-full-screen application, such as Gedit or a terminal window and no web browser application running. So far the trouble goes away when I close all of my web browser application windows but I saw it happen (only once) while there were no web browser application running. The web browsers I happen to use, which seem to trigger the glitch are Seamonkey suite, Firefox and Palemoon. I haven't used any other graphical, GUI browser.
In case you'd suspect my laptop, I saw this glitch happen on another machine that I used with nouveau. It doesn't happen when I use the proprietary blob from nvidia.com — and, no, I don't want to switch to the proprietary driver so don't suggest that.
Does anyone have an idea what causes this annoyance and how to get rid of it?