I have noticed strange behavior of my 2008 Expedition seat belt warning lamp and chime. I have not disabled the system in any way but the last few times I drove the truck, have discovered that if I unbuckle the seat belt while the vehicle is moving, either the lamp will illuminate with no chime, or the lamp will illuminate then extinguish after a couple of minutes.

In the past, the system would always alert me via chime and dash warning light if either of the two front seat belts were unbuckled with the vehicle moving. Now, the chime and light will illuminate only if the seat belt is unbuckled shortly after starting the vehicle if its been sitting awhile, but if I've been driving for some time, the behavior is as described above. Thoughts?