Here is what I believe is happening. Of course, diagnosing such a problem on a forum is less than optimal; it would be better hand on.
In a word, it's CoC.
When you point a riflescope at an object, the aptly named objective lens group (it's more than one lens), will focus the image on the first focal plane, just ahead of the erector tube, about where the turrets are. When I mean focus, I mean the image transmitted will be place there. The purpose of the adjustable objective (AO) is to perfectly focus the image of your object (target) onto the FFP so that you can see it nicely. When the objective lens is focused at a certain distance, there will be an area in front of the focus point and behind that will also appear to be in focus. This is called the focus field, the depth of this field, is also known as DOF or Depth Of Field. The extent of the DOF is determined by several factors including focal length, distance, F-stop and my favorite, circle of confusion or CoC. That last is essentially a measure of what you consider to be in acceptable focus.
Now in a riflescope, we have magnification, distance, objective size and zoom factor. When you focus your riflescope at an object at say 50 yards, you did so at low magnification. The field of focus at that distance will be a certain depth, which according to my experimental calculator will be from 43 yards to 60 yards. This means that your target will be in good focus for 17 yards. That also means that it's entirely possible that you are not focused precisely at 50 yards, but may be focused at anywhere between 43 and 60 yards.
Now, when you increase the zoom, you are also in effect reducing the value of the CoC, in other words as you increase the zoom the DOF reduces because you're bringing the image in closer and it is no longer in focus. So as you increase the magnification, you have to focus better because the CoC is smaller.
Also, you will have noticed that the closer the object is the more you move the AO. Going from 10 yards to 15 yards is a huge amount, but going from 300 yards to 500 yards is very small. It's a geometric progression, meaning as you get closer, it requires more movement.
Now, when you do it the other way around and focus on the object using maximum magnification, you are setting AO using a much smaller CoC, in other words, you are seeing the object much more clearly at high mag and set the focus much more precisely. As you zoom down, the object stays in perfect focus and only the DOF increases. Photographers make use of this quality all the time in all types of photography. They will use a short telephoto with a huge aperture to take pictures of a pretty girl nearby and thus set a very short depth of field that will produce an image where she is the only thing in focus and everything else is nicely blurred in what we call a bokeh.
Bottom line, when you're aiming close, focus on the object at a high magnification and then zoom down if you have to.
But let's see what Leupold says, there may be something wrong with your scope.
