prose citations do not collapse

[retroflexivity]

With an author-date style that has collapsing enabled, normal citations collapse properly, omitting the repeating author, but prose citations do not.

@jones1 @jones2

#cite(<jones1>, form: "prose") #cite(<jones2>, form: "prose")

#bibliography("ref.yml", style: "chicago-author-date")

gives this:

What I would expect is this, with the author appearing only once and years collapsed into the same parenthesis (at least this is what biblatex does):

(here's the yml)

jones1:
  type: Manuscript
  title: Foo
  author: Jones, John
  date: 2000
jones2:
  type: Manuscript
  title: Bar
  author: Jones, John
  date: 2005