I realise the Naza always flies "forwards" between waypoints set in Ground Station, but why does it make my F550 head into wind to maintain the track? Surely as a multirotor the track/heading correction is simple. There is no need for a multurotor to have a heading that is not on track. Have I set mine up wrong, or is this a flaw in the Naza?

It is not normal for the Naza to rotate the front towards the wind.  It will tilt toward the wind but should maintain heading.

joe@heliflightc Posted at 2015-5-7 20:48
It is not normal for the Naza to rotate the front towards the wind.  It will tilt toward the wind bu ...

Hi Joe, thanks for that... Mine definitely does. Almost all my Ground Station flying photos show a distinct opposite yaw on each pass. I cannot promise it is yawing into wind as I don't (currently) log the wind direction, but it yaws, and I can see in the resulting images that it gets worse at times and corrects itself, exactly as I would expect during a gust. For reference, we have the camera pointing straight down as we are mapping fields.

Try increasing your yaw basic gain a little bit.  
One of the big reasons for 3 axis gimbal is some yaw movement during flight particularly in windy conditions.  The pan axis stabilizes the images for some yaw drift in flight.
You may just be seeing normal expected yaw performance.