Mac Mail is hiding email addresses of recipients

Ok so all of a sudden when I get an email I cant see any of the other recipients email addresses. They are not hidden because they are BCC'd its just that they dont show up in preview or when you open the mail. However if you hovver over the blank space where they should be they then show up.

I've changed the preferences to show all member addresses, turned off smart addresses, tried the Hide Details section at the side of the mail, rebuilt the mailbox, quit mail ad started again but nothing seems to change it and I've no idea why its just started happening. ITS DRIVING ME NUTS.