As seen in the main development topic, if objects are not grouped nor inside a component, Sketchup assign face normals to all the vertices.
The results of this behaviour are shown in this thread.
As a workaround, or until a solution is found to integrate inside SU2LUX, I coded this tiny script to group all "ungrouped" faces in a model, with a corresponding feature to ungroup those faces to their initial condition.
Hoping it could be useful in some way.