Further to Belgique's post, if yaw is sensed with a vane (or perhaps differential pressure between the static ports), entering and exiting different flow regions within a wake vortex will likely feed fluctuating and misleading data to the yaw sensing system, resulting in confused yaw damper outputs.
The resulting aircraft response could compound the confusion.
If yaw in the A300 is sensed from ring gyros or other INS, then this theory goes out the window.
Obviously yaw damper and rudder programs need to integrate correctly sensed yaw as well as airspeed to limit rudder movements within the fin strength.
Once Airbus, NTSB and BEA have determined and made the necessary revisions, they should fly an updated A300 through the same flight profile to show that the problem truly has been fixed.