I think I found the solution for the "greyed-out top" view icon problem.
/usr/share/sweethome3d/sweethome3d.sh script contains, upon install via repository, the java option:

-Dcom.eteks.sweethome3d.j3d.checkOffScreenSupport=false

set it to true and top view icons behaves normally again.

Please let me know if I need report this to ubuntu launchpad or that this is the right channel