incremental build, with-lang dependencies ?

incremental builds work so well now its hard to remember how crap things
used to be, but there is one thing that bugs me sometimes. In a
--with-lang build if I add another language LANG to the list the on next
incremental build it will fail with
"workdir/Extension/wiki-publisher/description-LANG.txt": No such file or
directory.

I just hack things by touching that file and continuing. There is some
other similar issue to the above but I forget what it is.

C.