Re: Yosemite GM released - discuss issues, etc. here
I got a Mail update on 09/22, and since then I’ve experienced a few glitches with Mail. Minor stuff, really, like the icon badge (Mail dock icon) not always updating to reflect new mail, and a really pesky issue where sometimes clicking on an email in the 2nd column (sort by column) does not cause the email contents to be displayed in the message reader pane. When this occurs, I have to double click on the email, which causes it to open in a separate window.
Those two issues do not appear to be any better with this. Of course, OS X Mail has always had some wonkiness. *sigh*