Nick, thank you for your hints, I have checked them and could find the error.
If you select the V5 option in Central, you will of course only see the things that are suitable for V5.
Vector for V5 can be recognized easy by the missing height module in the configuration tool.
My mistake was that I installed the Base Pack first, but then the open LCs, HD Buildings, Trees and finally Vector.
But exactly this led to the display problems with entries at wrong places in the scenery library.
So I uninstalled everything except Base, then install again Vector and so on.
Meanwhile I have installed and checked all my Orbx stuff - everything looks normal.
Wolfgang