To fix this problem, use a leveling device to confirm that the roller shade tube is level. If not, adjust one of the brackets up or down until level is achieved.
If that doesn’t solve the problem, unroll the shade a few inches past the point where the shade currently stops, and slide a small, folded piece of paper on the OPPOSITE side end from where the shade is telescoping. Then, check for level.
If the shade is still not level, a second or third piece of paper can be used until telescoping disappears.
Please note that slight telescoping is normal. It only becomes a problem when the fabric comes in contact with the brackets, clutch or window frame.
Here is a video that covers this process: