Interesting you say that. . I too had an e-mail glitch recently but hadn't linked it to the latest OS update. In my case Mail was indicating unread messages in my inbox but none were visible. Doing a search for 'unread' showed them up and when I moved them to the inbox (even though some of them claimed to be there already) they became visible. At this point a whole lot of Yahoo mail from the previous day came flooding in. Since then things seem back to normal.
Maybe one of the housekeeping actions (eg rebuild mailbox) would help?
I rebuilt my mailbox 5 mins ago nothing yet.
The few I have left are very random.
Aug Oct Jan nothing else.
See you Valentines night. Wife not very happy!
Having to have lobster & champagne for lunch.
Graham Whent 