[Aalwein]

Each bag has four graphics:

  <Mapping ArtAssetID="bag" FileName="Invisible.tga" /> 
  <Mapping ArtAssetID="bag_normal" FileName="Invisible.tga" /> 
  <Mapping ArtAssetID="bag_pressed" FileName="Invisible.tga" /> 
  <Mapping ArtAssetID="bag_rollover" FileName="Invisible.tga" />

Try changing the other tags to the same graphic (unless you want different images for rollover and pressed).