The output of the WTJSON writer is rootless, which strictly isn't valid JSON.
Creating a XML writer via createIXmlWriterExt with e.g. WTStandard, produces rooted xml output.
Consequently, special handling of the JSON result is required to parse it, e.g. ptr_noRoot can be passed to createPTreeFromJSONString in order to parse the result.
The default behaviour should be to produce valid rooted JSON, with an extra flag/type to produce rootless JSON where required.