Trouble viewing calendar events on F1 mailboxes

We have recently moved all our users email to Office 365 and they have been assigned Office 365 E1 or F1 licenses. Now I see that users with E1 licenses using outlook can't open calendar events on users with F1 licens. All mailboxes have accessright set to default reviewer, and everyone can see eachothers calendars and events. The only thing not working is opening an F1 users calendar events using outlook. If an E1 user goes to Exchange online they can open the events of F1 users just fine. 
Is this intended behavior or is it something I can fix?