FC6, Evolution 2.8.3 with all updates, using against Exchange, groan. IMAP accounts, too.
Lately, when using message preview against messages either from the Exchange server or IMAP mailboxes, a message preview will freeze. I can open the message and carry on but the preview never comes refreshes/finishes. I tried turning preview on and off again, still stuck.
Gets better: try to kill client, grays out, never dies. Use the 'X' for a force kill dialogue, never happens.
Kill with killev, the UI dies & the backend processes die -- and then restart. I've use kill -9 and they still restart.