A little while back, I had an issue with Outlook not properly displaying the calendar in meeting invitations. It looked like this (which I’m sure you’ll agree is less than helpful):
The issue was the same whether I was in the viewing pane or opened the invite, and persisted regardless of whether I’d responded or not. There was no option to mouse-over to expand. The issue would disappear if I switched to another theme while an invitation was open in the viewing pane, but it would reappear as soon as I switched to another email or invitation.
Having tried some other fixes, such as starting Outlook in Safe Mode and creating a new profile – none of which helped with the issue at hand – the issue was finally resolved by repairing my Office installation.