I have just run a git diff, and I am getting the following output for all of my approx 10 submodules
diff --git a/.vim/bundle/bufexplorer b/.vim/bundle/bufe
To ignore all untracked files in any submodule use the following command to ignore those changes.
git config --global diff.ignoreSubmodules dirty
It will add the following configuration option to your local git config:
[diff] ignoreSubmodules = dirty
Further information can be found here