Yep, that resolved it for me, @epriestley.

I ran into this and dug in a bit. It looked like the data was getting truncated, so I turned on CURLOPT_VERBOSE in HTTPSFuture.php. I noticed that the Content-Length header was getting set to the same value (39, for me) every time curl did an outbound request - even though strlen of the JSON body was something around 200.