Can't assign user.name to "E F" in git config

I've never done a git init and I don't have any .git directory in the current directory. I get warnings in the following example. Moreover, I can't assign user.name to "E F".

humpty@wall:~/work$ rm ~/.gitconfig
humpty@wall:~/work$ git config --global user.name A B
humpty@wall:~/work$ git config --global user.name C D
humpty@wall:~/work$ git config --global user.name "E F"
warning: user.name has multiple values
humpty@wall:~/work$ git config -l
user.name=A
user.name=C
humpty@wall:~/work$ cat ~/.gitconfig
[user]
        name = A
        name = C

However, everything works fine here.

humpty@wall:~/work$ rm ~/.gitconfig
humpty@wall:~/work$ git config --global user.name A
humpty@wall:~/work$ git config --global user.name C
humpty@wall:~/work$ git config --global user.name "E F"
humpty@wall:~/work$ git config -l
user.name=E F
humpty@wall:~/work$ cat ~/.gitconfig
[user]
        name = E F

The same behavior can be reproduced after doing git init and by removing the --global option.

Is this an expected behavior or is it a bug?