Given that you really shouldn't be at 140kts in Conf 1 or 2 on approach I'm assuming you mean the phenomena where if you use speedbrake on the approach the speed settles above Vapp for a while. There won't be any reference in the FCOM because it's a defect. We encountered it when we introduced the 319 several years ago after many years experience with the 320. It can be fixed by a software mod.