title: Git submodule detached head state
body: <p>I've added 2 submodules to a project, subA and subB, in externals/subA and externals/subB.</p>
  
  <p>Today another team member committed his code and when it is pulled, both subA and subB show detached head status when using <code>git status</code> within externals/subA and externals/subB.</p>
  
  <p>I did <code>git submodule update</code> first and that reported no errors. I tried then <code>git submodule init</code> and <code>git submodule update</code> again but it did not change.</p>
  
  <p>How can we get the submodules back to be in sync? What causes this for the submodules? This is first time problem has arised since we began. Thanks.</p>