I'm not all that familiar with that radio, but if its like any other radio,
gunk can get around the buttons and cause them to stick midway.  If you dont
have any alcohol swabs, try isopropyl on a cuetip and go around the button
then work the button in and out abunch of times until its free moving.  Its
ok to get too much in there. The more the better really.    The usual
cautions apply. aka    no smoking, dont drip it on other surfaces...etc....
your working with a flammable liquid.