Sorry for the subject, the forum seems to cut off the subject when double quotes are used...
Try adding bypassupdates="false" to the a4j:support.
Thanks for your reply, joblini!
I tried using bypassUpdates="false" and it works now as expected. It works even without this modification, as bypassUpdates' default value seems to be "false" anyway. I guess I broke my earlier code somewhere else while experimenting...
However, I have one related question: I'm using the code from above in a <rich:dataList>. As I don't need to store the value of the selected item in my bean, I'm looking for a possibility to pass it to the updateFormat() method.