Created attachment 3601 
A screenshot of the grouped terminal windows on the xfce-panel

Using:
$ xfce4-panel --version
xfce4-panel 4.8.2 (Xfce 4.8.0)

$ uname -srv
Linux 2.6.37-ARCH #1 SMP PREEMPT Fri Mar 25 14:35:13 UTC 2011

OS: Arch linux

Summary:
When window grouping is enabled for the xfce-panel selecting a window from a "grouped window list" no longer changes the window focus when clicked.

Steps to reproduce:
1. Right click panel and select properties
2. A window called "Window buttons" will appear. Under "Behaviour" set "Window grouping" to "Always". Now close the window.
3. On an empty workspace launch 2 terminals (xfce terminal emulator).
4. On the xfce panel you will see a "window button" that shows that the 2 terminal windows have been grouped together showing "Terminal (2)".
5. Click on the window button and it bring up a list showing the two individual terminals. See the attached screenshot.
6. Try click on one of the terminals in the list.

Notice that the window focus doesn't change!!!

This shouldn't happen. When you click on a window in the grouped windows list focus should switch to that window.

Current workarounds:
1. Don't use grouped windows
2. Use scroll wheel on grouped windows button on xfce-panel.