Comment 58 for bug 214366

Thunderbird 3.0
Can't move folder to "Deleted" if a folder with the same name already exists.

 Move "test" to "Deleted"
 Create new folder "test"
 Move second "test" to "Deleted"
 Error: Folder already exists

Ideally, the second "test" folder should be moved to "deleted" as "test(2)" or something.