I have looked into the function while
Dash board -> Appearance -> Themes -> Install Themes -> Upload.
(and use Browse to say the file to be uploaded.)
After hitting 'Install Now', FTP dialog appears. When this dialog appears and before typing anything, the file specified is already in uploads
directory in server.
If the transfer is PC -> server type, FTP transaction may not be necessary.
My purely experimental patch works for me. It has one hardcode as 'themes'
so that this patch won't be good for general use. I will take a look to fix this problem, but please look at my patch if you have time. thank you.