[CentOS] vfstp and renaiming of files with ftp client

Hi,

I have a vsftp server and two users for up and download.

If user Alice uploads a file, the owner is set to Alice as expected
"-rw-r--r-- alice ftpuploadgroup"

Now Bob can login to the same folder and is able to rename the uploaded
file.

Bob can also rename an uploaded folder, but can't rename a file in that
folder ....

I'm confused, as I don't get why this is possible at all.

Some vsftp magic? :)

Can someone explain that to me?

    Thanks and regards . Götz