2.11.15 debug help / detached beam

[Jay Anderson]

I'm getting this in a file that used to compile pre 2.11.15:

Preprocessing graphical objects...
programming error: no skylines for alignment-child

continuing, cross fingers
Segmentation fault

I have the problem somewhat narrowed down to a couple of measures. Is
there a way I can make it spit out more information? I'm pretty sure
I've read something about this, but I couldn't find it. The verbose
flag doesn't give me anything extra in this part of the output.

In any case I've been using \set Score.skipTypesetting to narrow it
down. If I just do those measures by themselves I don't get a
segfault, but I do get weird results with a triplet and a slur where
the beam is detached above the slur. I tried this with normal eighth
notes, but they didn't cause this error. Here's as short as I could
get it:

\version "2.11.15"

\paper
{
 ragged-right = ##t
}

\score
{
 \new PianoStaff
 <<
   \new Staff = "RH"
   {
     \time 2/4
     \clef treble
     r4 s |
   }
   \new Staff = "LH"
   \relative c
   {
     \time 2/4
     \clef bass
     <<
       {
         \times 2/3 {bes8( bes' ees}
         \change Staff=RH
         \times 2/3 {g ees' bes')} |
       }
       \\
       {
         s4 \change Staff=LH r4 |
       }
     >>
   }
 >>
}

Thanks!

-----Jay