Inconsistment Message Deletion Policy
When you delete a folder you make it to piggyback the Trash as a subfolder.But 'Empty Folder' option does not move the messages to Trash but empties it permanently overriding the 'Move To Trash' behavior.
I believe you should make 'Empty Folder' to move all items to Trash folder.
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Deepak Vasudevan
http://thamizhththendral.blogspot.com/