05 Sonata radio issue

my parents bought an 05 Sonata GL V-6 last year. its only factory installed option is a sunroof. it has no other options dealer or otherwise installed that would effect the radio. it has about 19000 mi on it. a few months ago we all noticed that the radio would sometimes stay on after the car was turned off. the headlights do this too until the drivers door is opened then they turn off. anyway the radio sometimes stays on until the lights go off and sometimes it doesnt. its a sporadic issue which leads me to believe its not intended from the factory to do that. has anyone else had this happen to them? if so is it a big thing to worry about? if it is, is there someting that can be done?