It seems that if instead of

    darcs move a b

you do

    mv a b       # whoops!
    darcs mv a b

The "post-facto" darcs mv will DWIM[0].  This isn't clear from
move_description, which should change.

[0] There is one exception: a post-facto "darcs move a b/" where b/
    has not been added to the repository.  While dealing with this
    ticket, check that the error message in this case is helpful, and
    if not, file another bug report.

On Tue, Aug 04, 2009 at 01:25:59 +0000, twb1 wrote:
> [0] There is one exception: a post-facto "darcs move a b/" where b/
>     has not been added to the repository.  While dealing with this
>     ticket, check that the error message in this case is helpful, and
>     if not, file another bug report.

I'll just clarify here that just 'darcs add'ing b/ without also
recording that add does not help either.