I am having some problems with a revision of the airport LOWI Innsbruck for FSX. Using the Stock FSX airport I have saved this to a Project file. I then changed the altitude from1900ft to the correct one of 1907ft. I see, in the newly created scenery file there is no cvx file but the airport background shows in FSX. I then tried to delete this background using a Terrain Polygon, Exclude General, Airport Background. Compiled, in FSX the background had disappeared, great thought I. Back in ADE I then created a new Terrain Polygon, Airport Background, Flatten Mask Class Map ExcludeAutoGen. Compiled, however in FSX the background appeared as the 'original' and not as the new one. I tried adding Terrain Polys to this 'original' but with no success, it still showed as the 'Stock original'. Any ideas as to what I am doing wrong ?