I have a user that has 3 full mailboxes shared to them, so that naturally includes the calendars for those mailboxes.

When that user receives an invite for something, they have the ability to select which calendar it accepts for, but it always seems to default to a shared one, instead of their personal one. I cannot yet find a way to change this, and I don't know why this is happening to begin with.

Can someone point me in the right direction please?