Bad vertical spacing with instantiated staves

[Timothy Lanfear]

> I'm not top posting.

I tried 2.17.16 and found vertical spacing was much looser than 2.16.2 when 
instantiating ossia staves. 2.17.14 was the first release to exhibit this 
behaviour. The effect is only seen when the music extends over more than one 
page, hence the large repeat unfold in the example.

\version "2.17.14"

{
  c''1 
  <<
    c''1
    \new Staff c''1
  >>
  \repeat unfold 120 c''1 
}