Trouble with FUNCTION CODE with push-button when activating a DYNPRO

Hi, I've created a couple of PUSH_BUTTON in a few DYNPRO in XI for ABAP. In every case the problem was when I tried to activate the Dynpro, in that moment the value input in the field FUNCTION CODE was deleted automatically. After that, when you run the program, the variable SY-UCOMM has no value for every push-button. Thanks