repeats and alternatives

[James Bailey]

I don't understand alternatives. Can someone explain to me what I'm doing 
wrong. Why does the first example not compile properly with the excuse, "more 
alternatives than repeats" but the second example compiles just fine?

\version "2.12.3"

\book {
\relative c'' {
   \time 3/4
   \repeat volta 2 {
      g4 g8 g g4  |      
   }
   \alternative {
      { \repeat unfold 4 { g4 g8 g g4 } } |
      { \repeat unfold 2 { g2. } }
   }
   g2.
}
}

\book {
\relative c'' {
   \time 3/4
   \repeat volta 2 {
      g4 g8 g g4  |      
   }
   \alternative {
      { \repeat unfold 4 { g2. } }
      { \repeat unfold 2 { g2. } }
   }
   g2.
}
}