I have experienced in a couple of NPAs with base turn flown in FINAL APP that the airplane descended below the FAF altitude and caught the vertical profile whilst still in the base turn and well outside of the 1/2 dot of the radial inbound of the procedure. APPR was armed leaving the IAF (VOR). The procedures were perfectly coded in the FM database and where verified during the approach briefing. By reading the answer from Airbus to mi68guel that makes sense and could have possibly avoided that situation *BUT* chances are that the airplane would have been higher than 150ft on profile once established on the radial inbound and FINAL APP would have not engaged. In the remaining 95% of the NPAs that I flown I have never had any issue by arming APPR when cleared for the approach as per Airbus Sops. Regarding APVs, here as well never had any issue provided that the coding of the FM database was correct which is of course a precondition to fly the approach.
Cheers.