Description of problem:

  A sequence of
     git config x.y v1
     git config --unset x.y
     git config x.y v2
  leaves two [x] sections in .git/config.

Version-Release number of selected component (if applicable):

  git-1.5.5.1-1.fc9.i386

How reproducible:

  100%

Steps to Reproduce:
   mkdir test.git
   cd test.git
   git init
   sed -n '/m4rker/,$p' .git/config
   git config m4rker.foo v1
   sed -n '/m4rker/,$p' .git/config
   git config --unset m4rker.foo
   sed -n '/m4rker/,$p' .git/config
   git config m4rker.foo v2
   sed -n '/m4rker/,$p' .git/config
  
Actual results:

   [m4rker]
   [m4rker]
           foo = v2

Expected results:

   [m4rker]
           foo = v2

Additional info: