We will check this problem. However, if you use any GUI-based FTP client software, you should be able to easily drag and drop files to another folder. If you have DriveHQ FileManager 4.0, you can also easily drag and drop files.
Otherwise, you can also use the web-based service; you can simply cut & past the files using the web-based toolbar.
If you have to use command-line FTP, you can copy the file and then delete the original.