Quick question concerning my reverse light indicator

Ok just did a quick test, I unplugged the reverse lights from the back and now the radio will stay on when you put it in reverse. Plugged the reverse lights back in and radio will shut off when putting it in reverse, any thoughts? To much power draw at once causing the radio to loose power for a second? I will check it with car running tomorrow noght to see if it changes. No wiring has changed from the old to new radio, honestly I haven't noticed it before, i dont think i ever have pulled the car out of reverse and put it back in reverse with the radio on until tonight