I always think of it as: whichever tale is fluttering, the mast is blocking the wind on that side. So you would need to sheet in or fall off a bit to get the mast out of the way of the wind.

If the lower tale is streaming, but the top is fluttering, the head of the sail must be twisting off a bit; kind of the nature of boomless sails with no vang or traveler to pull it down flat. You could always sheet in harder and head up, if you want to go that way.

All that being said, in Rick's book he say's it's okay for the windward tales to dance just a bit, as long as the leeward ones are streaming. So you're not doing anything wrong. Right Rick?