I cannot select multiple items in the mail queues any more. I'm not sure which version introduced this, but I could with older version 5 Zimbra.
Tested with IE8 & Firefox 3.6.3

When I click first item, the selection just disappears, so focus is not even held on one line.
I need to requeue or delete hundreds of items after a spam-attack, so going through and deleting items one-by-one is kind of .... Well, you know what I mean.

I can select multiple messages in the bottom messages list, but there I cannot resize columns anymore.