gazebo 9 city_sim floating primitives

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I cloned the repo of city_sim from bitbucket and ran the simple_city.world. Everything looks really great; only there is a strange occurrence when adding models via the GUI. The models seem to hover above the ground; and this occurs for the primitives as well as other models. See picture. C:\fakepath\floating_sphere.png

Any idea on how to correct this? Gravity is turned on; when positioned high above the ground, models fall but stop short above the ground; as though there is some invisible plane.