Mauro, those are typical results of a boolean on a low poly model. The blue edges have soft normals and can be hidden, leaving only the black edges visible which have hard normals. Moi converts every poly face to a nurbs surface so to fix the topology, you would need to manually fix the Ngons of the polygon mesh to make them all quads. A lot of people avoid using Booleans in polymodelers until the very end because of this time consuming process. Ngons and Booleans are difficult to work with on curved polygonal surfaces.