When I have an activity (say appointment) and I assign it to
somebody else, everything is as expected.

However, if the organiser is changed to another person first
and then the owner is being changed, then after
assigning the appointment to that other person makes CRM
pop-up another assign-screen. If you press Cancel on this
screen the owner is already changed.

My question is, when does the Assign(To) screen pop-up
twice, only if the organiser is changed on forehand?