No need to change your driver in this case, this is all expected behavior. If you want to get the cubemap into a format that can be cropped, you need to convert it to a 2D texture. You can do this with the CubeMap TOP, which can convert it to a vertical cross 2D texture.
@Aval you wanted to do an immersive projection in some kind of cube space and you needed to crop the images to each side to a different projector, right? You should use after that a cubemap TOP and select the method CubeMap to vertical. It transforms this cross image to a 2D texture, the dimensions stay the same. Then you can crop the image as you wish. Pay attention that you get 4 extra squares on the cornesrs of surface where nothing happens. It’s just to fill the whole rectangle, because TOPs always need to be rectangles.