STEPS TO REPRODUCE
1. Read "ADDITIONAL INFORMATION" below, it might be needed to use the same Task Manager Settings as me.
2. Have at least two open windows of the same app (tested and confirmed with 2x Firefox, 2x mpv and 2x Spek) next to each other in Task Manager and a single open window of some other app (tested with Dolphin and "Task Manager Settings - Plasma").
3. On Task Manager, drag a tab and drop it between two tabs of the same app. Example: Task Manager initial order: Dolphin, Firefox, Firefox. You move Dolphin between the two Firefox windows, so now you have Firefox, Dolphin, Firefox.
4. Do a normal click (click and release) over Dolphin tab in Task Manager.

OBSERVED RESULT

The clicked tab unexpectedly changes its position in Task Manager. Example: it was Firefox, Dolphin, Firefox. I clicked Dolphin tab and now it's Firefox, Firefox, Dolphin.

This only happens in the first click on a tab that was manually rearranged between two tabs of the same app. Further clicks work as expected, until you move the tab again between two tabs of the same window, then the next click on the moved tab will again produce unexpected result.

EXPECTED RESULT

A normal click over a tab in Task Manager should just activate or minimize its window, without rearranging items. Reordering tabs in Task Manager is only expected when dragging a tab.

SOFTWARE/OS VERSIONS
openSUSE Tumbleweed Wayland
KDE Plasma Version: 5.26.3
KDE Frameworks Version: 5.100.0
Qt Version: 5.15.7

ADDITIONAL INFORMATION
My "Task Manager Settings > Behavior" settings, might be needed to reproduce the issue:
- Group: Do not group
- Sort: Manually
- [ ] Keep launchers separate (unchecked)
- Clicking active task: [x] Minimizes the task (checked)
- Middle-clicking any task: Opens a new window
- Mouse wheel: [ ] Cycles through tasks
- Show only tasks: [x] From current desktop & activity
- When panel is hidden: [x] Unhide when a window wants attention
- New tasks appear: To the right.