Was forced to change my Yahoo mail interface in July 2013 by Yahoo again to no avail. The new services is absolutely unusable. Switching back to the old interface is no longer available.
Poor performance of Mail service and untested Beta Mail interfaces have plagued Yahoo for over a year!! Already READ mail appears UNREAD for example. If this is to do with replication and frequent recovery, Yahoo ahs lost the plot. No longer do I use the service.