Ties in alternative endings

[Patrick Karl]

The NR deals with certain problems with ties in alternative endings, but I 
haven't seen a solution to the following problem:

\version "2.12.3"
\relative c' {
        a' b c d~
        \repeat volta 2 { d e f g }
        \alternative {
                { a, b c d~ }
                { a1 }
        }
}

The tie of the last note in the first alternative ending is not engraved, 
presumably because LilyPond sees that the next note, the a1 in the second 
alternative ending, is not the same and thus no tie is possible.  The only way 
I see to deal with this at the moment is to replace the tie with a 
\laissezVibrer.  Is that right?

There's actually another, related problem with this snippet.  If I change the 
note in the second alternative ending to a "d1", then LilyPond happily engraves 
a tie between the last note of the first alternative ending and the note in the 
second alternative ending.
I don't see an easy way to get LilyPond to deal with this problem correctly.

Help!