I've come across a wierd little error. The symptoms are as follows.
When the display message number is set to display 100 messages at a time, I can log in and I see my inbox right away, I can compose and click different tabs and everything works fine, however when I click on a different folder ie. an RSS feed folder or trash or junk and then click back on my inbox, nothing is displayed. If I go back to my preferences and set it to 50 messages, then everything works properly and I can navigate to different folders and what not and I cannot reproduce the error. Without logging out and back in, if I change the display back to 100 the original problem reoccurs. So for the meantime I will recommend to my users to display only 50 messages max. I'm about to see if there is a way to lock that through the admin panel. This is all through the web interface btw.