Sorry, lousy word to use. Yes I did mean that the longitudinally rigged sails were fluttering back and forth. In all cases I had a tail wind, but I only noticed the fluttering when the Bounty had problems moving (ie when FSTramp and/or tacpack was enabled). I had thought that the cause of this flutter was the wind direction, but the frequency of this flutter was pretty high (less than once a second).
Ah, thank you for that clarification.
Yes, if the wind is directly behind you, there is a slight wind direction variance by FS and as we switch from port to starboard on a 1 degree boundary, you will get this "flutter" as FS changes direction by a few degrees with each FS update.