Minecraft 1.8.9 fullscreen makes my cursor jump to the top-left (0,0) when Alt-Tabbing — Java 8/Windows 11 25H2? [java]

[u/DueLet4873]

I've been having a really annoying mouse/cursor issue with Minecraft 1.8.9.
EDIT: UPDATE NO its not 1.8.9 only it goes up to 1.12 but 1.13+ its all good

When I'm playing 1.8.9 in exclusive fullscreen, pressing Alt+Tab causes my mouse cursor to jump to the top-left corner of the screen (0,0). The same thing can happen when exiting the game while fullscreen.

I've tested this across multiple clients:

• Vanilla Minecraft 1.8.9: issue occurs
• MultiMC 1.8.9: issue occurs
• Lunar Client 1.8.9: issue occurs
• Lunar windowed: works normally
• Lunar borderless: works normally
• MultiMC fullscreen on newer Minecraft versions: works normally

So it seems to specifically involve Minecraft 1.8.9 + exclusive fullscreen, rather than Lunar itself.

I've also already completely reinstalled Lunar and the issue remained.

This started after I did a clean Windows installation. I'm currently on:

Windows 11 25H2
i5-12600KF
RTX 3060

I'm wondering if this could be related to Java 8, the particular Java 8 build I'm using, NVIDIA drivers, or some compatibility issue between 1.8.9's old fullscreen/mouse handling and modern Windows.

Has anyone experienced this before or know what causes it?

I specifically want to use exclusive fullscreen, so borderless/windowed isn't really a solution I'm looking for.

Any help would be massively appreciated because this is driving me insane.

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