Estimating the scene geometry from a single image is highly challenging and remains an unsolved problem. As such, you can find subtle artifacts like this in most of the results. The artifact that you are referring to stems from a geometry adjustment step in which we make sure that salient objects like humans or animals are on a plane in the 3D space. This requires image segmentation which is also highly challenging and may lead to parts of the background being assigned to the segmented foreground object and vice versa.