From experimenting, it looks like using sessions with session.use_trans_sid=1 will force your output to be buffered regardless of this setting.
My guess is that this is so PHP can hunt for URLs in your output to automatically add the Session ID to them. It must wait until script output is complete before it starts that replacement, rather than doing it "on the fly".
When i comment out my session_start() line, i get continuous output to the browser. Put it back in, and i only see the page when it's completely loaded. Change session.use_trans_sid = 0 and i get continuous output again.
