[racket] linking to planet packages in scribble?

I'm trying to fix the documentation for one of my projects (Moby) so
it has a hyperlink to another PLaneT package.  I tried something like
this:

    ... @racketmodlink[(planet dyoo/js-vm)]{js-vm}  ...


However, when testing this out, I saw that I was getting runtime
warnings during raco setup:

#########################################################################
raco setup: WARNING: undefined tag in <planet>/dyoo/moby.plt/3/10/manual.scrbl:
raco setup:  (mod-path "(planet dyoo/js-vm)")
#########################################################################


and the hyperlink that displays is red, and unlinked, so I don't think
it worked.