My .rc file contains a valid JSON starting with a square bracket:

[
  { "hello": "world" }
]

And rc outputs the following:

{ '[': true,
  '{ "hello": "world" }': true,
  ']': true,
  _: [],
  configs: [ '/Users/tobiasreich/Sites/Rosid/.rosidrc' ],
  config: '/Users/tobiasreich/Sites/Rosid/.rosidrc' }

I tested the strip-json-comments module and it's not causing this problem. I guess it's because rc tries to merge the JSON with the defaults.