I am not sure if this is an ArduCopter, mavlink or mavproxy issue.
I am using mavproxy to load a mission to ArduCopter (tried 3.6.7 -3.6.10).
My waypoints are of high precision (cm accuracy, so 7 about decimal places). When the waypoints are loaded, the mavlink messages displayed on the console are correct. However, when I read the waypoints using wp list, the waypoints are only correct to the first 4 decimal places.
I would think this is because the mavlink message fields for lat and long are float32 (and I require double precision) yet, when loading the same mission from mission planner, the waypoints are loaded correctly.