Desktop zoom triggered by scrolling on the panel or app menu when mouse wheel modifier is disabled

Distribution

Linux Mint 21.3

Package version

6.0.4

Graphics hardware in use

Reproduced on two systems, one with an NVIDIA GTX 1080 and the other with Intel integrated graphics

Frequency

Always

Bug description

If the desktop zoom mouse wheel modifier is disabled, scrolling (with no modifier keys pressed) on the app panel or in the menu causes the screen to zoom in/out.

Steps to reproduce

1. Go to Accessibility > Visual tab > Desktop Zoom
2. Enable Desktop Zoom and set the Mouse wheel modifier to "Disabled"
3. Move the mouse cursor over a blank spot on the app panel (taskbar) and scroll up. Alternatively, open the app menu and scroll up (it doesn't seem to matter where the cursor is positioned in this case)
4. The magnifier is triggered and the screen zooms in.

Expected behavior

The zoom should never be triggered via mouse wheel if the mouse wheel modifier is disabled.

Additional information

I was able to reproduce this on a live image of Linux Mint 21.3 Cinnamon, so that rules out any addons or 3rd party software causing the behavior.

Start by reproducing the issue with Desktop Zoom enabled and the mouse wheel modifier set to Disabled, testing both the app panel and menu on Cinnamon. Trace the desktop zoom input handling and the panel/menu scroll paths; done means scrolling without modifier keys never triggers zoom while normal zoom behavior remains available when configured.