Hi Andy,
sorry for the late feedback.
Could there be an encoding issue with http:request post requests? I send.. let $r:=<http:request method='post' > <http:body media-type="application/x-www-form-urlencoded" method="text">a=3&b=4</http:body> </http:request> return http:send-request($r,"http://posttestserver.com/post.php%22)%5B2]
You may be successful by additionally encoding "&" as "&" (didn't try it, though):
let $r:=<http:request method='post' > <http:body media-type="application/x-www-form-urlencoded" method="text">a=3&amp;b=4</http:body> </http:request>
Christian