git submodule update is not recursively called when adding a git submodule

Steps to reproduce:
1. create git repo Y which contains a submodule pointing to git repo Z
2. create a new git repo X
3. add submodule to X that points to Y
Note, that the repo Z will not be updated (directory is empty)
Console output from adding submodule (repo names changed):
git -c diff.mnemonicprefix=false -c core.quotepath=false submodule add -f git@git.assembla.com:Y.git sireal.sdk
warning: templates not found /usr/local/git/share/git-core/templates
Cloning into 'Y.sdk'...
git -c diff.mnemonicprefix=false -c core.quotepath=false submodule init Y.sdk
Completed successfully