Django inline edit of model with FilePathField

Question

I have this simple setup:

class Artist(Model):
  ...

class Download(Model):
  artist = ForeignKey(Artist)
  title = CharField()
  file = FilePathField(...)

and the admin looks like this:

class DownloadInline(TabularInline):
  model = Download

class ArtistAdmin(ModelAdmin):
  inlines = [DownloadInline,]

I get a validation error for the Download inlines every time I try to save the Artist record. The Admin seems to think I'm trying to add new Downloads to the Artist, even though I haven't filled in the "title" fields - the FilePathField gets preset to a filename by default and there's no way to set it to None.

Is there a way around this or am I doing something wrong?