Hi there,
I wish I could give you a solution, but I am also similar/same behavior, although I am not parsing any JSON data (my codec is 'plain'), I'm simply reading the HTTP response code returned in the response.
In my scenario, a 503 will work correctly (presumably because I'm simply checking the code rather than parsing content), but if the web server is unreachable and http_poller times out, this is when I get the same behavior which you're seeing.
It appears as though 'type' gets cleared, and any tags are overwritten with '_http_request_failure'
Thanks