There was something bugging me about this example, and I couldn't place my finger on it - then I remembered - I blogged about doing something similar:
http://weblogs.java.net/blog/driscoll/archive/2009/07/a_tale_of_two_c.html
So, this is (probably) not a bug with Mojarra, but rather something to do with what you're doing.
But I have a guess: you're doing something like <form id="form" prependId="false">. So in that case, ":result" doesn't refer to the component, rather, ":form:result" refers to the component - the rendered id on the page isn't matching the in-memory id of the component.
It's best when using ajax tags not to do a prependId=false on naming containers - it confuses things.
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