2013 CX-9 that I just got yesterday. the dome light is set to "door" (middle) but won't turn on when you open the door. The light works if you move the switch to "on", just not when set to "door"
I have noticed this problem too. I think it's the middle row light in particular, that won't come on with door open. Seems like the behavior has NOT been consistent, cause cause I remember not being able to track it down.
I don't know if the new 2013 CX-9 is like my 2007 but if it is make sure that the front dome/map light switch is set to door otherwise the second and third row lights will not work. The second and third row dome light are individually controlled but they're main power source comes from the front dome/map light. In a sense the front light is the master switch to the other two. Hope that this helps and that it is your issue.
2013 CX-9 that I just got yesterday. the dome light is set to "door" (middle) but won't turn on when you open the door. The light works if you move the switch to "on", just not when set to "door"
make sure the second and third row lights are also set to "door" or "on" - I forget which since the car is not with me now but check both of the individual lights -