This is a known characteristic of the A320 family, particularly the 319.
If, after arming APPR on the FCU, you use the SPDBK the aircraft will tend to settle at up to 10kts above the VAPP. Simply take the TL out of the CLB detent, disconnect the ATHR, rearm it and then reset the TL to the CLB detent to reactivate the ATHR. The ATHR will then control speed to the VAPP. Alternatively, use manual thrust.
I don't know why it happens and it is not referred to in the FCOM. My company has asked Airbus why it occurs but, to my knowledge, we have had no reply yet.