Save and then open causes reflections around tangents to disappear
Construct a pair of parabolas, get their common tangents, choose one tangent and unselect "show object" from the other(s). Reflect the two foci around the shown tangent and save. When the project is re-opened, all tangents appear and the reflections of the foci become undefined. (Occasionally, the reflections can "jump" to be around a different tangent.)
I am attaching the a ggb file, as well as a screenshot of what the project looked like before I saved it.