Ähm, i see, the bmaps for button off and button over are both the same, so you should change it. actually only the bmap for button click changes, and i think you cannot click and see its changes without a function defined which the button shall call.
from the manual
button(x, y, bmapOn, bmapOff, bmapOver, functionOn, functionOff, functionOver);
edit: ah, ok, the bmaps are ok.
but maybe has to do with the flags? translucent and overlay?
Trie it with show only