Problems rebasing branch after renaming files

Hi list, I ran into a problem, and I'm unsure it's a git bug or a misuse of mine.

Here's the scenario:

1) Have the master branch and a branch called A

master
|
|----- A

2) Work more in master

master
|
|----- A
|
|

3) Create branch B and work on it. In this branch, rename a directory
containing source files with git-mv

master
|
|----- A
|
|----- B

4) Merge B to master

master
|
|------ A
|
|
|
|

5) Rebase A to master

master
|
|
|
|
|
|----- A

I found that, checking out A, my files in the now renamed directories are as the were in B, i.e. not including the changes made in A, because I have rebased A to master and git didn't realize that the files in old_directory_name are the same as in new_directory_name so they should have been merged.

Either this is a git bug or not, can anyone suggest a way to fix this? All I've thought so far is to git-format-patch the patches that I had in A, use sed to replace the old_directory_name with the new one, create a new branch called A2 at master's head, apply the patches there and git-branch -D A.

Thanks!

PS: please CC me as I'm not on the list.