Originally Posted by
sonicbum
The PM will then use the MCDU as needed.
Apparently the fleet office is quite happy with the statistics of this SOP. There have been in the past events where the crew mainly changed from DES to V/S and that lead to the troubles. The mitigation strategy was to prohibit the use of V/S when descending/climbing "via" a STAR/SID and the use of step FCU altitude selections. My bet is that the latter will be removed soon as, again, it does not make sense if things are done properly from the beginning.
It may have happened due to incomplete understanding of DES mode and constraint compliance. Easier to explain that than device more complicated solution.