Clock applet preferences does not allow editing of custom format

Thank you for your bug report, I can reproduce this here.

I have passed this bug report upstream.

http://bugzilla.gnome.org/show_bug.cgi?id=413114

the bug has been fixed upstream now

This upload fixes the bug:

 gnome-panel (2.19.2-0ubuntu1) gutsy; urgency=low
 .
   * New upstream version:
     Panel
     - Code cleanups
     - Force the panel to not be restarted when there's already a panel
       running, fix endless loop of error dialogs
     - Add a checkbox to let the user choose to not restart the panel if
       there was a problem registering with bonobo at startup
     - Default the "Applet disappeared" dialog to reload
     - Default the "Can't load applet" dialog to not delete
     - Small HIG improvements to the launcher editor
     - Fix alignment of the run label in the run dialog
     - Fix creation of launchers with empty spaces in the command
     - Fix the launcher editor to not save a full-path icon for the
       non-localized icon when it's not needed
     - Fix gnome-desktop-item-edit work for relative URI when creating a
       .directory file
     - Use the launcher icon as a fallback for launchers without an icon
     - Guess the icon when the user enters a command in the launcher editor
     - Use macros for name icons to easily change the name of named icons
       when needed
     - Check whether reboot is enabled in gdm (and not only shutdown) and
       only show the buttons when they're useful in the logout dialog
     - Prefer /var/run/gdm_socket as path for the GDM socket
     - Take into account NAME_MAX for the length of the filename when
       guessing a name for launchers in gnome-desktop-item-edit
     - Fix creation of launcher when dragging an URL with ? or :
     - Make some error dialogs visible in the taskbar and make some other
       transient to the panel
     Clock Applet
     - Don't display tasks that are marked completed
     - Update the clock when the configuration tool exits so that the user
       doesn't have to wait up to one minute to see the change
     - Fix preferences window to not hide the custom format when it should
       be shown
     - Document that the custom format is the format used by strftime
     - Show the date by default in the applet
     - Let distributor easily specify their configuation tool instead of
       hardcoding everything
     - Update the clock every second for UNIX format
     - Make Internet time work a bit better
     Notification Area Applet
     - Fix compiler warning
     Misc
     - Install data files in $(datadir)/gnome-panel/ instead of
       $(datadir)/gnome/panel/ (Vincent)
     - Add --with-clock-time-utility configure flag
     - Run gtk-update-icon-cache on uninstall
     - Make .desktop file used for bug-buddy translatable
   * Sync with Debian
   * debian/application-default-icon.png.uue:
     - default icon for the menu entries.
   * debian/control.in:
     - Build-Depends on liblpint-bonobo-dev, liblaunchpad-integration-dev
     - gnome-panel Recommends menu-xdg instead of Depends on it
       and Recommends alacarte
     - gnome-panel Suggests fortunes-mod, it's used by the fish applet
     - maintainer is the Ubuntu Desktop Team
   * debian/gnome-panel-data.install:
     - updated and install the "About Ubuntu" menu item
   * debian/gnome-panel-data.p...