bmap_for_screen (screen_shot_map, 1, 0);
wait (1); // wait 1 frame until the bitmap can be saved
//perhaps you need only one frame?

game_save (app_name, 0, SV_INFO + SV_BMAPS);

//perhaps this is the issue ?
Unlike a pointer, a handle to an engine object
survives saving/loading
and contains the same value at every run of the application.