update_submodules duplicates

I'm trying to replicate git clone --recursive in pygit2, and this is the function I've come up with.

def get_submodules(repo, creds):
    submodules = repo.listall_submodules()
    repo.init_submodules(submodules=submodules)
    repo.update_submodules(submodules=submodules, callbacks=creds)
    for submodule_path in submodules:
        submodule = repo.lookup_submodule(submodule_path)
        sub_repo = submodule.open()
        get_submodules(sub_repo, creds)

The problem I'm having is that in certain circumstances, this will cause crashes. Let me paint the picture.

Master Repo

1. Submodule A
2. Submodule B
   2.1 Submodule A
   2.2 Submodule D
3. Submodule C

When update_submodules attempts to run on Submodule A the second time, it crashes. Not completely sure how to get around this. Some repos are in this format, but I haven't found a workaround. Any thoughts?

Start with the get_submodules example and the repo.update_submodules and repo.lookup_submodule calls. Reproduce the nested layout where Submodule A appears more than once, then inspect how repeated updates are handled. Done means the recursive operation no longer crashes for that layout, with the behavior verified against the reported scenario.