Order of applications change after closing the last-but-one item of a group

Submitted by DarkTrick

Assigned to Xfce Bug Triage

Link to original bug (#16071)

Description

Reproduce:

• Create new panel
• Add Window-Buttons
• Window Buttons -> Settings -> Window grouping: Always
• Window Buttons -> Settings -> Show button labels: turn off (only icons are shown)
• Window Buttons -> Settings -> Sorting order: "None, allow drag-and-drop"
• Close all dialogs
• Start mousepad twice
• start thunar
• <The order of applications inside the panel should be "mousepad","thunar" (two buttons)>
• left-click on mousepad -> close one of the two instances.

Expected:

• One instance closes; Nothing else changes.

Actual:

• One instance closes; Icon moves to the right.

Version: 4.13.4