thanks for the info skwasjer. It turns out the problem is with the outer Turm. If I 'hide' the outer turm the little annoyance stops. Once I let the outer turm be visible again the little annoyance returns. Now the Turm, err Ship, writing I did for the C3 worked with no problems at all. The C3 uses 1 map for the hull, the VIIb Turm I outer uses 3 maps. It might have something to do with this. The mystery deepens...
