Why isn't the dome light on my 2015 F150 going off when the door is closed?

My daughter just purchased a used 2015 F150 XL Supercab and I noticed the dome light wasn't coming on hen the driver's door was opened.  I found a button to the right of the dome light that appears to control whether or not opening the doors turns the light on and the symbol and word "OFF" were lit.  I assumed that pushing this button and getting rid of the lighted "OFF" would result in the dome light coming on when the door was opened, but instead the dome light came on, started to dim then brightened again, then dimmed then brightened again (and so on and so forth) without ever going off completely.  She clearly can't drive at night like this because the dome light is so bright and the alternative is to not have the dome light come on at night which, for me, is a safety concern.  Has anyone experienced this behavior before?  Any ideas?