Yes, robbiej ,
Similar thing we can see for the gzip response -- any ref to response(eg. ${response.mainpart}), any operation on response(eg. "Response must match xpath"), will make gateway to store the response, uncompress it, parse it...
So, the streaming will not work, or the gzip response cannot go through without uncompress.
The "Audit message in policy" assertion with "Always" save response option can cause the same problem.
message-completed global policy itself won't cause the problem, only if there is any assertion ref to response.
"Traffic Log" is the same, if the traffic log doesn't save response, it won't cause problem. If you want to log the response for most of other policies, there should be a work around -- if Cluster wide property trafficlogger.selective=true, traffic is logged only when the ${trafficlogger.select} context variable is defined in a policy and its value is "true". ie. you can disable traffic log for those policies using streaming.
Regards,
Mark