Outlook 2013 not removing expired drafts

Question

We've just set a user up on a new Win7 64-bit PC with Outlook 2013.

Outlook is saving a draft of every email she is composing, but never deleting the draft after the email is sent.

She has about 30 emails in her drafts folder.

Why is this occurring?

Answer 1

About 2 hours after this problem occurred, we restarted the machine, and the problem disappeared.

It may of been the Exchange sync had completed between client and server (it was a 1GB mailbox).