rebase -p confusion in 1.6.1

Hello all,

While trying to understand "rebase -p", I came across some very unexpected behaviour that made me throw in the towel and ask for help!

The outputs I got really confused me.  Before the "rebase
-p", the tree looked like
    
    * 78ffda9... (refs/heads/work) b4
    * be1e3a4... b3
    *   cd8d893... Merge branch 'master' into work
    |\
    | * 0153c27... (refs/heads/master) a4
    | * 74f4387... a3
    * | f1b0c1c... b2
    * | 2e202d0... b1
    |/
    * b37ae36... a2
    * ed1e1bc... a1

But afterward, this is what it looks like -- all the "b" commits are gone!

    * 0153c27... (refs/heads/work, refs/heads/master) a4
    * 74f4387... a3
    * b37ae36... a2
    * ed1e1bc... a1

What did I do wrong/misunderstand?

Here's how to recreate. Note that "testci" is a shell function and "lg" is a git alias. They are, respectively, (1) testci() { for i; do echo $i > $i; git add $i; git commit -m $i; done; } (2) git config alias.lg log --graph --pretty=oneline --abbrev-commit --decorate

    git init
    testci a1 a2
    git checkout -b work
    testci b1 b2
    git checkout master
    testci a3 a4
    git checkout work
    git merge master
    testci b3 b4
    git --no-pager lg   # graph before rebase -p
    git rebase -p master
    git --no-pager lg   # graph after rebase -p