On the 319 it is nearly a "standard procedure" to add 2 -3 kts extra on the Vapp, as it does not hold it's speed. Does not matter even if in fairly calm conditions! It will even fluctuate/flicker below Vls if nothing is done. I personally prefer NOT to sit and wait and see what might happen or how low it might go, as I am not paid to be an Airbus test pilot!
The ATHR disconnect in the FCU does work, it goes momentarily into THR LOCK until engaged again.
I never saw this problem on the A320 with IAE engines, but I did see it also on the A320 "sharklets" with CFM engines.
No idea if any connection between this, just my observation.