JSON - YAJL parse error

I am attempting to parse a JSON formatted string from within a RPG
REST web service server program. The parsing is done via Scott
Klement's YAJL wrapper.

The web service is called from an IBM i node.js client as a HTTP 'put'
method. Since I'm passing a JSON string in the request body I have to
set the 'Content-Type' header. However if I set the Content-Type to
'application/json' I get this YAJL error: “lexical error: invalid char
in json text”.

Here's a sample of the JSON - externally validated as valid JSON.

{"pm_option":"ZZZ","pm_branch":"999","pm_accno":"AAA1234567ZZZ","pm_snma1":"PPP","pm_trnamt":"10.78","pm_cash":"N","pm_payee":"A.N.Other","pm_wthacc":"","pm_wthscdc":"","pm_wthrefc":"","pm_taccn":"","pm_tsnma1":"","pm_demand":"N"}

If I now set the Content-Type to 'text/xml' YAJL doesn't complain and
parse works fine.

I get the same results if I run the web service call from SoapUI so
the error is not caused by the node client.

Any suggestions as to the cause?

Thanks,

Keith