when loading files from the gui interface, the types of molecules in the file is auto-detected and the appropriate representation chosen.
This _only_ happens when a (pdb) file is loaded from the gui, not when a pdb entry is fetched from the net or a file is specified via the commandline.
What's worse, autodetect sometimes fails (e.g. on single amino/nucleic acids e.g. guanosine) and no molecule is shown.
Please make it an option in GUI to switch between default and autodetected representation.