I see that you put your
testvaluein toevoeging.men, so you should test in the c:when on the same value. Or are you storing the men value in another bean-attribute?
It would be helpful if you send us the code of your bean so we can see what happens because ajax tries to validate the whole form at once, so there is something wrong there. Try first if it improves when you put the
attribute in a:support. This prevents sending the whole form.