git-bundle behaves unexpected with submodules

I am the author of a script: https://github.com/najamelan/git-backup

I am using git bundle to back up git repositories. In recent versions of git the repository metadata of a submodule are stored in .git/modules of the parent repository.

When git-bundle is ran in a submodule, it creates a bundle of the parent repo, omitting the information from the submodule, thus effectively not backing it up.

Anyone who can shed light on this?

thanx in advance
naja