This is mentioned in one of the safety first magazine issued by Airbus
If it helps
On A300/A310, A320 and A330/ A340 Families,
• The VFE value displayed on the PFD
is based on the slats / flaps con- trol lever position and it moves by one step as soon as this lever is moved.
• The overspeed aural warning trig- gering threshold varies according to the actual aircraft configuration, i.e. the slats / flaps surfaces real time position.
Therefore, during slats / flaps tran- sition, the dynamic acceleration of the airplane may lead to a temporary OVERSPEED WARNING even if the current speed is out of the red and black strip displayed on the PFD. In this situation, there are neither opera- tional consequences nor safety issues.[