Perhaps this is by design, but it was a breaking change for us. JToken.Parse (and other Parse methods in LINQ to JSON) now parse date strings as type 'Date' instead of type 'String'.
 
The workaround is to create the JsonReader ourselves and set the DateParseHandling property to DateParseHandling.None, or to use JsonConvert.DeserializeObject<JToken> and set the same property on JsonSerializerSettings.