item property reverting to plain text in notification

I have a strange thing occurring in multiple workflows across my SharePoint site. Whenever I have a workflow notification, if I have put an Item Property in the subject line of the email, for example "Created By", rather than having the name of the user, it just says the name of the Item Property (Created By) in the subject line. The item properties work fine in the body of the email, just not in the subject line. Please help!