Comment # 4 on bug 905348 from Andrei Borzenkov

(In reply to Werner Fink from comment #2)
> I've no time to hunt this bug. Is there any volunteer around here? IMHO the
> shell function _minimal does not handle the directory case of the value of a
> variable.

No. There are two chains - for $FOO and $FOO/.

The former call chain is _longopt => _init_completion => _variables. It
actually does everything right, but completions that are using _longopt also
add filename context (-o filenames) which seem to cause bash to quote content
of COMPREPLY. Default bash completions do not set filenames option or
explicitly unset it if current word looks like variable expansion.

The latter explicitly quotes argument in _filedir.

I'm afraid there is no simple fix. _filedir should probably split string on
'/', add initial part as prefix and complete only final part. But look at zsh
_path_files to get an idea what it involves ... 

The actual question is - why systemd completion requires bash-completion at
all? On the quick glance it does not use anything from its framework.