Incorrect calculation and presentation of certain quadrics
Certain quadrics are drawn incorrectly. In this example the red elliptical cone badCone is rendered with what appears to be some kind of sign error when computing the surface.
Adding points on the surface is also affected: point A is added to the "wrong" surface of badCone. Substituting the point's coordinates into the original equation shows that it doesn't satisfy it: the number named shouldBeZero should be zero (surprise!) but it isn't.
The green cone sometimesGoodSometimesBad is initially drawn correctly. It depends on a slider to vary the coefficient of the y^2 term, and with the coefficient equal to 1055 it is OK, but varying the coefficient shows that the bug manifests randomly for some values of the coefficient.
Geogebra 5, Geogebra 6 and the web version are affected all the same.