Weird behavior of shell variables in git aliases

It seems that a variable is available only once?! How can the following shell session be explained:

    $ git config alias.test0
    !echo $1
    $ git test0 foo
    foo
    $ git config alias.test1
    !echo $1 && echo $1
    $ git test1 foo

    foo
    $ git config alias.test2
    !BRANCH=$1 && echo $BRANCH && echo $BRANCH
    $ git test2 foo

    foo

Thanks, D.