After mate-screensaver blacks screen, input causes screen contents to be visible for a few seconds before showing unlock prompt

I regularly observe this behaviour on one particular system: * I lock the screen either manually or by idling for the configured time * screen turns black and shortly after the screen enters power-save * I try to unlock it by pressing a key or moving the mouse * **screen turns on, but *without* the screen lock, showing the regular desktop** * I can move the mouse and see the cursor move * windows display a fresh image (not the one when the screen should have locked) * after **a few seconds** something remembers that the screen was to be locked and **then** hides the regular desktop and shows the password prompt * entering the correct password then correctly unlocks the screen I have never seen this before and I run basically the same setup on most of my systems, past and present. And I have not seen this happen with the same system on a different physical screen. This is currently more of a nuisance but I worry about it also being a security problem. Potentially this might allow people without the correct credentials to unlock the system permanently. The system is set up as this: * Linux kernel 6.7.12 * debian trixie/sid * lightdm * mate as session manager * **mate-screensaver** (default) * xmonad as window manager (replacing marco in mate) * LG screen and a (somewhat older) AMD/ATI Radeon card I suspect lightdm mate-screensaver to be the culprit but **I don't know how to troubleshoot this**. I also have only observed this with the specific LG screen, but what the system decides to display in this context should theoretically not depend on what screen is plugged in.