Mounted partition's side-pane item doesn't have `Unmount` icon

Version information

Thunar 4.8.11

Calculate Linux (Gentoo-based)

Current behavior

The mounted partition's side-pane item doesn't have the Unmount icon:

At the same time, it has the Unmount context menu item:

For comparison: the SFTP-host item has both the icon and the same Unmount context menu item.

Expected outcome

The mounted partition's side-pane item have the Unmount icon.