Erratic window focus

I've noticed what appears to be erratic window focus on the mail app. If you have two apps open, mail and safari say, with safari having focus, if you click the mail list or a message body, Mail, doesn't always regain focus, in the same way that safari and other apps do when clicking anywhere in the window. I find you need to click the window top frame to do this; although this isn't a guarenteed solution and times when you do this, click else where and the window moves to that location.

I thought I saw this with Word also, but I'm not 100% as I've not spent enough time playing with it.

Anyone else seen weirdness like this?