STL file format does not preserve hierarchical relationships between geometries. To be able to use imported STL geometry nicely in Visual Components applications geometry should to be post prosessed.
There are three commands that you need to execute.
1. Select all the geometry sets belonging to the imported geometry and execute "Merge Sets" command. This merges all the geometry sets into one.
2. Merge boundary points within some tolerance so that the geometry set will not contain any gaps.
3. Re-organize geometry set into logical pieces using "Decompose Geoset" command. This will go through the originating geometry set and put all the neighboring polygons into new geometry sets.