-Hover the mouse over an e-mail in the right-side panel. (The e-mail’s sender should just be a long e-mail address including an ellipsis.)
-Hover the mouse over the sender’s e-mail address to preview the contact details window.
-Try to move the mouse over the Details link.
When the mouse goes over the date next to the sender’s e-mail address both preview windows close.
This issue also appears to affect e-mails displayed in other places, too.