After the update to 5.8.4, using the mouse wheel over the sound applet in the tray to change the volume also switches open windows (I'm using the icon-only task manager).
This affects the whole system tray, a wheel event switches to another virtual desktop.
I'm using Plasma 5.8.4 on Debian sid as it landed there yesterday and I also getdthis issue when using the scroll wheel on the KMix icon, which makes it actually quite unusable. I also notice that accidentally using the scroll wheel on certain native Plasma 5 widgets that do not handle it (the Networks and Clipboard icons) triggers the same behavior. Plasma's own PulseAudio-based audio volume icon (which I don't normally use) seems unaffected -- perhaps it's because it handles its own wheel events? In previous 5.8.x versions, using the wheel on the Show Hidden Icons arrow or the tiny empty space between tray icons also triggered a desktop switch, which I personally found a bit annoying and counterintuitive as there's a separate Pager widget for this kind of thing.
As per the comments, scrolling switches virtual desktops, not open windows. FWIW scrolling on the sound icon still changes volume, but it simultaneously changes virtual desktop. Changing the volume with the mouse is basically unusable now. Other icons also trigger this bug, e.g. Kalu, NetworkManager, caffeine, and the integrated triangle that opens the pop-up menu.
Could be caused by https://commits.kde.org/plasma-workspace/95a8a620248d96ca089c222689605042e27e8fb5
(In reply to Christoph Feck from comment #4) > Could be caused by > https://commits.kde.org/plasma-workspace/ > 95a8a620248d96ca089c222689605042e27e8fb5 Reverting that commit indeed makes the issue disappear.
I can confirm that reverting those patches fixes scrolling on icons (I tested the volume icon, NetworkManager, caffeine). However, scrolling over the triangle that opens the menu still scrolls the virtual desktops. I'm not sure if that is the intended behaviour. (It's not a big deal anyway, because unlike the volume icon, there's no other intended behaviour on scroll for it.)
Plasma 5.8.4 on Gentoo. I can confirm that reverting the commit mentioned in comment #4 fixes the issue (with the exception of "menu triangle" behavior).
Actually, perhaps related to the "menu triangle" issue, if I slightly miss the icon for (e.g.) the volume control and scroll, I still get this bug. For example, if I place the mouse cursor around the red arrows in the following screenshot. https://i.imgur.com/9uQ04Z6.png
*** This bug has been marked as a duplicate of bug 372957 ***