@ BlindPete

It seems strange that TOPO has a display 3dTerrain (DEM) or 3dbuilding (gmap3d),or which may render the 3D Terrain/3dBuilding of other map (CN)

Try disabling the gmap3d.img or DEM and see if it behaves the same.

If you post a screenshot we can better understand.Tnx...

Bye,bye