When using --depth=1 with submodules, git tries to clone a submodule. Let's say its master branch to the depth of 1. However the super project does not point to a branch but to a sha1, so except when the master branch points to sha1, it will fail.
Most often you can get away with --depth=100 or something like that, but what's really needed is a way to fetch a sha1 and not only branches and tags. This is however not as easy at it seems, since only sha1 that are accessible from any tag or branch should be allowed for fetching (otherwise we've a security hole).
I'm not sure if this is implemented in git yet, and I'm not sure if all git hosting providers support it.
Most often you can get away with --depth=100 or something like that, but what's really needed is a way to fetch a sha1 and not only branches and tags. This is however not as easy at it seems, since only sha1 that are accessible from any tag or branch should be allowed for fetching (otherwise we've a security hole).
I'm not sure if this is implemented in git yet, and I'm not sure if all git hosting providers support it.