Evolution makes a "click" sound twice on certain actions

Binary package hint: evolution

Using evolution, I stumbled upon the following strange behaviour: when the "click" sound is activated in gnome's sound preferences, most buttons act normally and correctly (which is: one click sound on each mouseclick).
However, the category switching buttons (Post, Calendar, Contacts, Memo's, Tasks), which are displayed in the main windows, do make twice a click sound when you hit them. So:
* Make sure the "click" sound is activated in gnome's sound preferences
* Open up evolution
* Hit the "Calendar" button when you are viewing your mails (1)
* You will hear the click sound twice

(1) You will hear the click sound only once when you hit the "Calendar" button, when you are already in the Calendar module (or Contacts, mail, ...)

Most of the times, the second "click" sound goes together with the updating of the GUI.

Using evolution & evolution-common 2.21.5-0ubuntu1 and evolution-data-server 2.21.5.1-0ubuntu1 on Ubuntu Hardy Heron.