custom headers illusory urlrequest/urlstream controlling slight get?

quite rudimentary really:

var req:urlrequest=new urlrequest();
req.url="http://somesite.com";
var header:urlrequestheader=new urlrequestheader("my-bespoke-header","1");
req.requestheaders.push(header);
req.method=urlrequestmethod.get;
stream.load(req);

yet, i check trade wireshark, my-bespoke-header being sent. i change urlrequestmethod.post insert information req.data, following header sent, nonetheless receiving concentration requires post.

the support mentions blacklist headers sent. my-bespoke-header these. it's presumably value mentioning imagining ask opposite pier same domain. zero reported policyfile log, seems unlikely, nonetheless something remedied force loading crossdomain.xml allow-http-request-headers-from notwithstanding fact crossdomain issue? simply an undocumented underline peep actor wholly send tradition headers post request?