• alice select bob as her delegate
• alice shares her inbox and calendar with bob
• carol invites alice
• bob reads the invitation in the inbox of alice and click accept (on behalf of alice)
• roundcube insert the appointment in bobs calendar, but NOT in alice's calendar
• bob can select which calendar to save in, but only between his own calendars (not the calendar of alice)

Bob should select alice's calendars to save the event into and invitation reply should be sent in the name of Alice, not Bob.