There are some discrepancies between multiple and non multiple option, regarding default value when no argument is set

Example :

  option "unique" - "set a 'unique' option" string typestr="STR" optional argoptional default="unique_default"
  option "multiple" - "set a 'multiple' option" string typestr="STR" optional argoptional default="multiple_default" multiple

Using a small test program, I see :

$ ./ggotest
unique: unique_arg=unique_default unique_orig=(null) unique_given=0
multiple: multiple_given=0 multiple_arg[0]=multiple_default
multiple_orig[0]=(null)

 >> expected

$ ./ggotest --unique --multiple
unique: unique_arg=unique_default unique_orig=(null) unique_given=1
multiple: multiple_given=0 multiple_arg[0]=(null) multiple_orig[0]=(null)

 >> oops ! I expected to see the same argument for both options.

This behaviour seems inconsistent, and unaligned with
the documentation :
"If it is known that a multiple option has a default value, then it can be safely assumed that the first element of generated array <option>_arg| is always set."