I can confirm that the clock panel item does not pick up changes made by "sudo dpkg-reconfigue tzdata" immediately, but after running "xfce4-panel --restart" it does.
There is a patch attached in the linked Debian bug report. It is probably worth to test it, and eventually forward it to the Xfce bug tracker.
Thanks for the detailed reply.
I can confirm that the clock panel item does not pick up changes made by "sudo dpkg-reconfigue tzdata" immediately, but after running "xfce4-panel --restart" it does.
There is a patch attached in the linked Debian bug report. It is probably worth to test it, and eventually forward it to the Xfce bug tracker.