Hi Peter, sorry for the delay.

>>>> We could enhance your original workaround like this:
>>>>
>>>>  am__remove_distdir = \
>>>>    { test ! -d "$(distdir)" \
>>>>      || { find "$(distdir)" -type d ! -perm -200 -exec chmod u+w {} ';' \
>>>> -         && rm -fr "$(distdir)"; }; }
>>>> +         && if rm -fr "$(distdir)"; then :; else \
>>>> +## On MSYS (1.0.17) it is not possible to remove a directory that is
>>>> +## in use; so, if the first rm fails, we sleep some seconds and retry,
>>>> +## to give pending processes some time to exit and "release" the
>>>> +## directory before we removed.  See automake bug#10470.
>>>> +              sleep 5 && rm -fr "$(distdir)"; fi; }; }
>>>>  am__post_remove_distdir = $(am__remove_distdir)
>>>>  endif %?TOPDIR_P%
>>
>>> This works, best so far!  Committable, if you ask me.
>>>
> 
Could you try the attached test case to see if it can reliably expose the
problem on MSYS/MinGW?  If yes, I'll prepare a patch shortly.

Thanks,
  Stefano