clock applet does not change displayed time on change of TZ

Status changed to 'Confirmed' because the bug affects multiple users.

On Mon, 2018-08-13 at 18:50 +0000, Launchpad Bug Tracker wrote:
> Status changed to 'Confirmed' because the bug affects multiple users.
>
> ** Changed in: xfce4-panel (Ubuntu)
>        Status: New => Confirmed
>
It is now even worse.

I changed the TZ from the top ribbon and:
1. Shell/date sees the new TZ, as before
2. The icon in the ribbon loses its display settings, both tooltip and
normal display.
3. If I try to reset things in the Properties menu the new settings
only remain until I close the properties window. They then reset to
null.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.5 LTS
Release:        16.04
Codename:       xenial
----------------------------

More info:

After a logout/login I still could not change the settings.
After removing the clock from the top ribbon and re-adding it worked
OK.

I have now changed the TZ back and again lost the display.

Changing any property seems a bit flaky. Sometimes it takes, sometimes
it does not. I tried to change the TZ back and lost it, removed/added
the clock and this time is took. I then had trouble changing the
display and tooltip formats. Eventually they took. No idea why it
sometimes works and sometimes not.

I am now in the strange situation where the clock thinks it is 12:53
and the shell thinks it is 14:53, with a new shell.  I shall try
another logout/login.
--------------------------------

After logout/login I still have different TZs in the clock on the
ribbon and in the shell. There is no TZ environment variable.

When I changed the TZ in the clock I did it two different ways. The
first time I used the drop-down list, and this lost the display. The
second time I typed the new TZ into the text box; this landed me with
the inconsistent TZ settings. Digging around, I see that /etc/localtime
has the wrong setting.

Another try:

Change the TZ using the geographic map, then select more accurately
from the drop-down. This sticks and is consistent with the shell.

I can change the display format OK.

Trying to change the tooltip format (defaults to custom with a blank
format) loses both the tooltip and the display formats.
--------------------------------

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.