When I call FeatureSet.FromJson(someJson), it seems that the resulting Fields property of the featureset is not set. I am wondering if this is a bug or behavior by design? The JSON string I tried comes straight from ArcGIS Server so I suppose that should be OK.
This also happens with the QueryTask, where the Fields property isn't set either. I suppose that the same code is used internally, so that would make sense.
I hope someone at Esri could comment on this.