2001 e150 dome light question
 

Hello, I bought a used 2001 e150 and have a question about the dome light operation. When I have the side slider door open, the dome light will turn off after about 15 minutes and that's great. But when I have the rear doors open the light will not turn off automatically. Is this normal or should the dome light turn off when the rear doors are open for a while?
Thanks, Trent