Comment #41 on issue 2801 by [email protected]: Patch: Approximates cross-staff slurs in VerticalAxisGroup vertical-skylines.
http://code.google.com/p/lilypond/issues/detail?id=2801
In there is single system output the SlurStubs should be suicided long before any of these callbacks return values.
David - could you confirm what single-system regtests you're talking about? I'll do some tests to see if stubs aren't killed off, but they should be suicided as soon as the cross-staff callback is called (which is before the vertical-skyline callback is called).
