Bug 514890

SUMMARY
Simultaneous Left+Middle mouse click causes permanent rubber-band selection that cannot be cancelled

STEPS TO REPRODUCE
1. Be on the KDE Plasma desktop (no windows, or windows minimized)
2. Press and hold Left Mouse Button
3. While holding LMB, press Middle Mouse Button simultaneously
4. Release both buttons

OBSERVED RESULT
A rubber-band selection rectangle appears and becomes "stuck" in permanent selection mode. The selection:
- Does not complete or disappear when releasing mouse buttons
- Cannot be cancelled with Escape key
- Cannot be cancelled by clicking any mouse button (LMB just moves the anchor point)
- Cannot be cancelled by Alt+Tab or switching windows
- Persists until KWin or Plasmashell is restarted

EXPECTED RESULT
Selection should either complete normally or cancel when mouse buttons are released.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian 13 (Trixie)
KDE Plasma Version: 6.3.6
KDE Frameworks Version: 6.13.0
Qt Version: 6.8.2

ADDITIONAL INFORMATION
- Mouse: Generic 3-button Bluetooth mouse
- Session type: Wayland
- Touchpad is automatically disabled when mouse is connected

Suspected cause: Race condition between selection start (LMB) and Primary Clipboard Paste action (MMB). The MMB interrupt seems to prevent the button release event from being processed, leaving the selection state permanently active.

Workaround: Disabling "Middle Click: Paste selected text" in System Settings → Workspace → General Behavior prevents the issue.