Steps to reproduce:
1 - Open multiple tabs inside a group.
Example 1. A group with two Word documents.
Example 2. A group with one Calc spreadsheet and a Writer document.
2 - Look at opened program icons in Taskbar.
3 - Hover mouse over active tab icon.
4 - Result - Taskbar only shows icon for active tab inside a group and window preview of active tab inside a group.
Expected result - icons for all active programs inside a tab should be visible in the taskbar. Windows previews when hovering mouse over taskbar icons should show all the instances of said program running in tabs and not only active one.