I modified tracker so that you add n files (and some
other classes) with one submit. But it doesn't work if
you try create more than one. Class instances are
created ok, but linking to 'owning' class fails. Only
one id is added to the multilink property.

I included a patch that seems to fix things, but I
might overlooked some conditions.

Problem with the original code (roundup/cgi/actions.py)
is that it each property can set only once (line 429).
So only the first id is added to the multilink property.