I honestly have never opened mine and would have to check but I'm going to say that in a lot of vehicles the rear door windows don't fully open. That is by design.
In most cases it's the shape of the door that prevents the window from going down all the way, The lower portion of rear doors are shaped around the wheel wells. The windows don't have room to go down all the way.
Since I can't remember the last time I opened rear windows I don't know how my current or last few vehicles were.
__________________ If you need a shoulder to cry on ... ... pull over to the side of the road!
Like stated above it's by design. Look at the width and height of the window and then look at the area of the door below the window - due to the rear wheel wells/ shape of the door - there is not enough width at the bottom half of the door for the window to go down all the way. This is very common. Some vehicles have a small triangle shaped window that does not move at all and the narrower square portion of the rear window is then able to roll down all the way.