thanks Drier and shortfuel!
Still it puzzles me that we have "independent" FMAs.
According to FCOM 1.22.30 p69 "the FMGS synchronises the A/THR, approach capability and AP/FD modes to provide identical information on both PFDs."
When we have AP 1 + 2, AP 1 is master. But aren't the FMGCs still synchronised? Is there here another 'transparent to the pilot' thing?