It's a geometry issue with the projector and screen. Its close enough so I wouldn't worry about it. The screen or wall your projecting on may not be flat. Try pulling out the lower left corner of the screen out a 1/2 inch and see what happens. The projector may be slightly too far to the right, rotate the projector to move the image to the right a inch or so and see if it fixes it. IF you have lens shift correct it back to center with it, if not you would have to move the whole projector to the left.
EDIT: of course the UHD50 doesn't have horizontal lens shift so correcting this could be a big hassle.
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