Rendering objects in array not supported by SimpleSchema@2 and uniforms

[Gervwyk]

With SimpleSchema@ objects in an array worked well. However, after updating to SimpleSchema@2, array objects are not rendered in the array UI. A good example is running:

new SimpleSchema({
    'a':     {type: Array},
    'a.$':   {type: Object},
    'a.$.x': {type: String}
})

in the demo where x is not rendered...