repeats, nested repeats and alternatives

[yota moteuchi]

Dear Mailing list

I have a bunch of questions about the repeat syntax I'll like to submit to you.
\version "2.11.28"

1) About numbering
here is a ordinar situation of repeat volta with an alternative : 

\repeat "volta" 2 {
    a b c b
}
\alternative {
    { e f e f }
    { e f e b}
}
c a e f
\break
d e a g
f e f a
e e g d

(the resulting output is the first staff of the joined pdf)
A problem is raised by the numbering of the measures... the first alternative shouldn't be counted but it is... so I corrected it manually

\repeat "volta" 2 {
    a b c b
}
\alternative {
    { e f e f }
    \set Score.currentBarNumber
 = #2
    { e f e b}
}
c a e f
\break
d e a g
f e f a
e e g d

(the resulting output is the second staff of the joined pdf)
Here, magically, the second alternative bar vanished... why ?!

2) About nested repeats
In the Hungarian March of Berlioz, there is many repeats and once in the piece the second alternative continues a during few measures which are themselves repeated. Here is a simplified example :

\set Staff.voltaSpannerDuration = #(ly:make-moment 4 4)
\repeat "volta" 2 {
    a b c b
}
\alternative {
    { e f e f }
    { \repeat "volta" 2 {
        e f e b
        c a e f
        \break
        d e a g
        f e f a
        e e g d
        }
    }
}

(the resulting output is the third staff of the joined pdf)
The problem here is obviously the spanner, far too long. While \set Staff.voltaSpannerDuration
 = #(ly:make-moment 4 4) don't change anything (and I don't know why !)

3) Collapsing alternatives
This is more a suggestion than a question but when dealing with big orchestral parts, the \alternative tag is very painful to maintain. Indeed, in some case, trumpets have the same alternatives bars (
i.e. alternative 1. and 2. are duplicates) and should/might be collapsed into one bar. While in the conductor it have to remain expanded (because flutes have different altenatives).
Could this automatic collapsing (and numbering) be implemeted easily or obtained via a tweak ?

Yota