I just bought a 2007 Trailblazer LS. When I lock the doors using the key fob or the door locks all the doors lock except for the glass door on the lift gate. When I open the l glass door and then close it, it locks. How come it doesn't lock along with the other doors?

My rear glass wont lock either but if I open it the alarm will sound. If I lock my keys in i can now just climb in and retrieve them.