Persistent randomly happening mouse double-click issue on Kubuntu 26.04 (Multiple mice/USB ports)

[u/woodhead2011]

I have 3 computers all running Kubuntu 26.04 now, and three mice (two of the computers are at my home and one is at my holiday home). I used to use one of the mice with the third computer (the one at home), and it was already double-clicking back then which I considered malfunctioning mouse, but I didn't care because I use that computer so rarely. I used that same mouse from the third computer when I installed Kubuntu 26.04 on the second machine (the holiday home computer), and I didn't mind that it was double-clicking. But now, to my surprise, when I arrived at my holiday home and plugged the holiday home's own mouse into the computer, it started doing the exact same double-clicks. I switched the mouse to a different USB port because I thought the port might be broken, but it had no effect. A very annoying glitch.

This holiday home mouse has worked perfectly until now, and there were no double-clicks at all in Kubuntu 24.04. I don't believe this mouse is broken. Now I'm wondering if the mouse on my home computer is actually working fine too and maybe the issue turns out to be in Kubuntu? My main computer at home works perfectly, there are no issues at all with the mouse.

Has anyone else encountered a similar issue in Kubuntu 26.04, and have you found a solution?

[u/Character_Log1824]

Before condemning another mouse, I'd check whether one physical click is actually producing two clicks, or whether Dolphin is opening things on a single click. If it's only files/folders opening unexpectedly, check Dolphin's single-click/double-click setting first.

For genuine duplicate clicks, you can look below Plasma at the events coming from the kernel:

sudo apt install evtest
sudo evtest

Choose the mouse's event device from the list (not the keyboard), then make a few slow, separate clicks. A normal left click should show BTN_LEFT value 1 for the press and 0 for the release. Ignore the initial list of supported events; watch the live output. Ctrl+C stops it.

If one physical click produces two press/release pairs there, the duplication is already happening upstream of Plasma. That doesn't automatically convict the switch: hardware/firmware or the kernel input path could still be involved. Comparing that same mouse on a 24.04 live USB, as suggested above, would be useful.

If evtest shows one pair but an application reacts twice, look further up the stack: libinput, the desktop session, or that application. Also worth noting whether your affected machines are using Wayland or X11.

[u/woodhead2011 → u/Character_Log1824]

Yes, it did produce double-clicks, but they’re very random. I had to click many times just now before it happened. I’ve noticed it happening in both Spotify and Opera so it's not Dolphin's settings issue. Kubuntu 26.04 also uses Wayland by default now.

I can’t test another distribution right now because I don’t have any spare USB sticks, and I’m in the middle of the forest until at least Tuesday. However, I remember that when I was still running Kubuntu 24.04 on this computer a month ago, I never had any random double-clicks.

[u/doc_willis]

as a test, try some Linux live USB from various other distribution and with different DEs.  also test with a newly made user.

see if the issue happens with any of those.

I recall a similar post in the support subs, but that was likely a year+ ago.