Just when many of us were celebrating the end of the mirror slap. Moving parts shutter weigh far less than the mirror, and shake is more noticeable?.
No just as CR guy says - because the camera is much lighter than your typical FF DSLR and with a longer lens attached via lens collar and foot, the camera is just hanging in mid air. Normally thats cool on a rock solid 1DX or whatever but somehow on the A7R it's floppin about when the shutter moves. Even the tiniest vibration can muck up a shot with a tele lens.
Mirror slap is not an issue with DSLRs on a tripod due to mirror lock option.
Another reason why the "big and bulky" mirror slapping DSLRs still have plenty of life left in them. There will always be something to be said about ergonomics and solidity.