There are two static ports on either side of the fuselage just ahead of the empennage.
The stall speeds at idle are:
Flap 0 - 54 KIAS
Flap 15 - 52 KIAS
Flap 60 - 51 KIAS
So the airflow at full power could be distrupting the static vent reading to give a higher IAS than the true CAS.