completion disturbed by other staff

[PálBenkő]

> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing on usenet and in e-mail?

\version "2.12.3"

<<
  \new Staff
  {
    b2 b b b b b
  }

  \new Staff
  {
    b4 b\breve b2.
  }
>>

\layout
{
  \context
  {
    \Voice
    \remove "Note_heads_engraver"
    \consists "Completion_heads_engraver"
  }
}