I spotted a glitch the other day and posted, concerning the inbox, then saw 'sent' message handling was worse (up / down to next / previous messages always went back to list of messages), and bumped that (though no sign of acknowledgement it was seen)...
Now the 'up' arrow is showing a "." (I was going to link to an image but it should be easy to spot) for both inbox and sent messages (once a message is being viewed, IYSWIM).
One day (2011) it may work. Just don't change the code while "under the influence" please, Tech bods, else your "clear thinking" and even any comments in the code will perhaps be "unclear" in the sober chill of a January morning.