\alternative fails if \repeat unfold proceeds it

I've run into something that I think is a bug -- or I'm not understanding
something.  It happens when you are in a \repeat volta section and use a
\repeat unfold just before the \alternative section.

\version "2.25.13"

\relative {
  c''4 c c c |
  \repeat volta 2 {
    \repeat unfold 2 { d4 d d d }
    % d4 d d d % uncomment me and everything's fine
    \alternative {
      \volta 1 { e4 e e e }
      \volta 2 { f4 f f f }
    }
  }
  g4 g g g
}

The work around is to have one line of non-repeated notes just before the
\alternative section.

--
Knute Snortum