Fwd: Possible bug: MMRs and keepAliveInterfaces

[Saul Tobin]

Originally posted to user list by mistake, sorry for doublepost to anyone
who follows both.

If any of the interfaces for MultiMeasureRests (e.g. rest-interface,
spanner-interface, multi-measure-rest-interface) are included in
keepAliveInterfaces (useful if you want to condense some systems in a
score, but not others), then when an MMR occurs on either side of a system
break it can cause staves to be kept alive that otherwise should be removed
due to keepAliveInterfaces = #'().

\version "2.19.82"

\layout {
  \context {
    \Score
    keepAliveInterfaces = #'(stem-interface
                             note-head-interface
                             rest-interface
                             )
  }
}

% Ex 1

\new Staff \with {
  \override VerticalAxisGroup.remove-empty = ##t
  \override VerticalAxisGroup.remove-first = ##t
} {
  R1
  \set Staff.keepAliveInterfaces = #'()
  \break
  c'1
}

% Ex 2

\new Staff \with {
  \override VerticalAxisGroup.remove-empty = ##t
  \override VerticalAxisGroup.remove-first = ##t
} {
  \set Staff.keepAliveInterfaces = #'()
  c'1
  \unset Staff.keepAliveInterfaces
  \break
  R1
}

Is this a bug? Am I missing something about the intended behavior of MMRs?
Ideas for workarounds or fixes?

Thanks!

Saul