I’m aware of the fact that a second channel is required to store lightmaps informations, but this data is only computed on lighting rebuilding and it shouldn’t make any difference in the “preview window”, should it? That also doesn’t explain why converting the model to Editable Mesh rather than Editable Poly seems to solve the problem.
However I already tried creating a second channel in 3ds Max or ticking “generate lightmap uv”, but the problem persisted. (The overlapping is wanted for texturing purpose)