It will be very convenient to provide handler for double-click action over clock to show Orange or other calendar application, or what ever user need. Now in XFCE it is not clear for newbies how to open calendar. Such option exists in number of panel plugins, and it nice because it is customizable. Default command could be run of Orange Calendar, as it is default for XFCE (I judge from point of Xubuntu 9.10 view).
This is a bug against Orage.
Created attachment 2749 screenshot of target plugin I spoke about this panel plugin, sorry for incorrect package name.
that is not orage panel plugin.
Added a hidden xfconf property to set a double-click command.
Devel branch has been merged in master. A 4.7.0 release will follow soon. If you think this bug is not fixed? Feel free to reopen the bug.