OK - I wish I had more details but I'm using rc11 for the server and Thunderbird for the client. I'm using Maildir and I'm doing server side folder delivery using Exim. On server side folders I'm seeing the count of messages in a folder showing 22 unread messages but the messages themselves don't show up. I deleted the index files and it still didn't show up. But then I restarted dovecot and now the messages in that folder are there. I've noticed similar behavior randomly ever since I upgraded to 1.1. The 1.0 never had this problem. Wish I had more details to post.
A little more information. One ove my server side folders became essentially inaccessable. The folder was empty. This folder is actually emptied by another process that reads and deletes the content of this folder. Using Thunderbird the message count showed as having 1 message but no messages showed up. I dragged a new message into the folder and that new message wasn't visible. I then restarted dovecot and the folder started behaving normally again. I'm going to download and install the latests to see if the bug goes away. Unfortunately it's not a consistent bug to reproduce.