Calendar Invitations

My wife and I use iCal/Calendar on our iPhones, iPad & Mac Book (all of which are running the most up to date software) which we share with each other and invite each other to appointments, however once I have accepted an invitation it remains as a pending notification in Calendar (screen shots attached). This is most annoying and the only way I can find to resolve this is to turn off the calendar in settings and then turn it back on. If anybody can help with this I would be very grateful.