metadata:foo or {metadata}{foo}

Following settings work well with \getvariables{metadata}{...}
\setvariables
    [metadata]
    [
      title={Bonus},
      author={scerac},
      date={\currentdate},
    ]

I find that I can't use \getvariables{metadata}{...} for following setup.
\setupdocument[metadata:author={scerac},
   metadata:title={Bonus},
   metadata:date={\currentdate}]

Are metadata:foo and {metadata}{foo} different?
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