We have one user that is experiencing weird behavior when deleting messages. Sometimes when they delete a message, their view changes to a different location. It has been reported that it sometimes moves the view to a different tab (Briefcase, Tasks, etc.) and other times to a different folder within their mail.

They have no filters setup, but move all mail out of their inbox to subfolders. These folders are NOT under the inbox, but are on the same level as the Inbox, Sent, Trash, etc.

The view in mail is set to reading pane OFF, so they have to double click the message to view it. This opens the message in an additional tab within Zimbra, not in a new window.

The following behavior has been observed.
From the mail tab, a message is double-clicked. It opens in another tab. The user clicks reply. After sending the reply, they click the delete button. Most of the time this works as it should - the view is back to the folder where the message was. About every 3rd time, it changes their view to somewhere else.

Once it went to the address book. The reply button is located staggered below the Address Book tab.
The rest of the times it acts strangely, it moves the view to the Briefcase. The delete button is located staggered below the Briefcase tab.

The only browser that I can confirm this on is Firefox 24.

The only things that I can think of are possible browser/ cache issues - maybe it is not remembering the last view correctly - or possibly when clicking the button it is also clicking the tab above it. If you delete the message and it immediately goes to the Briefcase, maybe there was some overlap of the buttons.
Now if you reply and it also clicks the Address Book, maybe it takes care of the reply, then goes to the last folder it was in (Address Book, based on the overlap).