hmmm, I remap props all the time..never have that problem....not flipping the map? not flipping the normals? not rotating the map? when making a tex, select all the black ( want selection tool ) invert selection to only be the mesh, not the white. grow the selection by a few pixels then make it another layer / object. that expansion really helps cut down on seam errors ( like no tex on the seam of the prop ) when resaving the obj, every setting for it has to match the map settings exactly. and you have to use the newly mapped obj as well for the prop. the texture information may be different for it after you map it.