Algodoo

Not weird at all. In fact, it's quite common. It happens because you either drew an object over a plane which happens to have the same collision groups enabled (in this case collision group "A" is checked on both the object and the plane), or you forced an object down below the upper surface of the plane. When you start Algodoo, the object behaves as if it were a ball being held under water. It will launch itself up to the surface very fast, but in the real world, the object doesn't jump out of the water more than a very short distance and then ends up floating on the surface. In the Algodoo world, an object launches way up in the air, practically in orbit around the Algodoo world!

You can do the same thing with any object. Make a box or a circle above the plane, and its collision layer will default to "A". Then start Algodoo, and with the Grab Tool, grab the box or circle and pull it below the surface of the plane by just a short distance and let it go. The object will launch straight up like a rocket!