There are only a few seconds you say between HDG pull and return to NAV mode?
Perhaps the waggle you see could be an auto flight system peculiarity to your aircraft type or company configuration. My earlier answer was based on a return from HDG mode to NAV after at least a few minutes.
That said, it still might be informative to see if the winds and any XTE relate to the direction of the course correction once returning to NAV mode.
Speaking of peculiarities, I believe someone told me when there is an AC bus failure on the Airbus, one of the ailerons or spoilers will raise a bit and this is "normal". I wonder if this behavior relates to the auto flight and is in some way connected to your waggle.