This PR adds a failing test case to the v5-dev branch.

The issue is that the registration method

def register(mf):
    mf.register_defaults({
        "annotation": lambda: 10,
        "annotation.bug": lambda: 10
    })

succeeds for the first line registering state["annotation"], but **fails for the second line registering state["annotation.bug"].

Merging this failing test because any further development of v5 should fix this issue first.