Percents repeats confused by polyphony

[Mark Polesky]

The first of a group of "full measure" percent repeat
symbols doesn't get printed when the music expression is
polyphonic (see the attached png); and the following errors
are generated:

programming error: must have Item for spanner bound of PercentRepeat
programming error: Multi_measure_rest::get_rods (): I am not spanned!

Also, a pdf file is produced, despite getting these:

error: failed files: "percent_repeats.ly"
shell returned 1

Here's a test file:

\version "2.13.18"
\relative c'' {
  \repeat percent 4 {
    << { c4 c c c } \\ { f,4 f f f } >>
  }
}

One workaround is to have the user manually add:

\set countPercentRepeats = ##f

...but I assume this is a needless burden.  I glanced at
percent-repeat-engraver.cc, but I still don't know any C++,
so I'm unable to solve it myself.  Is there a way to have
the countPercentRepeats context property set to #f by
default?  Or is the real problem some sort of flawed
assumption within the PercentRepeat or Multi_measure_rest
code?  I have no idea.

But I presume this is a bug which hopefully is easy to fix.

Any insights?
- Mark

percent-repeats.png
Description: PNG image