Finally, I have caught the bug! LOL

Exception in thread "AWT-EventQueue-0" java.lang.InternalError: Surface not cachable
at sun.java2d.xr.XRPaints$XRTexture.getAccSrcSurface(XRPaints.java:211)
at sun.java2d.xr.XRPaints$XRTexture.isPaintValid(XRPaints.java:224)
at sun.java2d.xr.XRPaints.isValid(XRPaints.java:75)
at sun.java2d.xr.XRSurfaceData.getMaskFill(XRSurfaceData.java:205)
bla-bla

You are right, but I don't understand why the bug was closed unfixed...

Nevertheless the Sweet Home 3D remains an excellent and useful program.

Thanks a lot!
Dmitri