Weird behavior of --delete option when downloading with trailing slash.

When I download from Amazon S3 using a trailing slash in the source address, s3sync tries to delete the whole directory that I am downloading. For example, suppose I upload first the directory dir:

./s3sync.rb -r --delete /root/tmp/dir bucket:pre

Here everything works fine and some keys pre/dir, pre/dir/file1, pre/dir/file2, etc are created in "bucket", whereas other stuff is deleted. Now if I try to download:

./s3sync.rb -r --delete bucket:pre/dir/ /root/tmp/dir

it downloads the stuff as it should, but it warns me with the message:

"Could not delete directory /root/tmp/dir: directory not empty"

This warning is not totally idle: if the directory happens to be empty, it erases it. It seems to me that this shouldn't happen. The above command should just copy the "files and directories" with prefix "pre/dir" to /root/tmp/dir, deleting files and directories in /root/tmp/dir that don't appear in S3, but not try to delete the directory /root/tmp/dir. I tried different variations on this, and the culprit seems to be the trailing slash /.