Simple POST requests are getting split into 2 frames

I'm working on an application for which getting the network latency down to a minimum is critical. I've noticed that when I use surf (with the curl_client) that for every HTTP POST request, I'm doing 2 complete round trips. (I'm already using a preexisting connection and have TCP_NODELAY enabled.)

From using wireshark, I can see that surf is first sending a HTTP frame with just the headers, waiting for an ACK from the remote server, and then finally sending the body (which is only about 20 bytes long).

As a workaround, I'm routing the request through a local HTTP proxy, which makes the ACK of the first frame very quick, and the proxy ends up combining the header and body into a single frame before sending it to the remote server, so I effectively only have 1 (remote) round trip.

Is there any way to force surf to send both the header and body in a single frame? Or if I'm misunderstanding something (quite possible), how can I further debug the extra round trip?