> How can I tell ClrMame to only include the files once in the Fix-DAT?
> and if this isn't implemented, could you please implement it? :)

A fixdatfile is just a subset of the used database/datfile. If they appear twice or more in the datfile and you miss the files and save a fixdatfile, they appear twice or more in the fixdatfile. Since double crc32s usually represent the same files it's the datfile author's fault that they appear more than once in the datfile. Equal checksums within a parent/clone relationship are rather normal, but they appear only once if you scan in split or full-merged mode and so they appear only once in the fixdat.
Of course I'm aware that the rebuilder will rebuilt all files even if listed once, so it might look useful to include them only once in the fixdat...but mainly a fixdatfile is an output of the currently missing files within different sets....

in other words...I doubt I will change the behaviour....the used datfile should be a bit more cleaner ;)
Although I did make a note about your idea...

Roman Scherzer
ClrMamePro