There is quite well known bug in AX that breakpoint placed in the clicked() method of a button will not be triggered. It is quite unpleasant one since when one faces it first time he gets totally confused.
However, there are easy workarounds for this bug. First one – put breakpoint into the method that is called from clicked (in most cases it is possible). But if not, keyword breakpoint can be used – it will be triggered in clicked() method.