permission changes not persistent, who is changing them back?

Hi all! If I change the permissions to a device in /dev (for example sr0 or usbscanner) , to be owned by the user "root" with and by a group, for example "scanner", or "disk", with "rw" rights, this change seems to get accepted. However, when I log in next time, the owner is set back to my username and the group to "users", and the "rw" rights of the group are taken away again. This is very ugly, it it not how I think a multiusersystem should be. I guess, I'm changing at the wrong place, I can't believe that that is the way it is. I'm currently running SuSE 8 and kde3.02, but I think I saw this also before on SuSE 7.02 and kde 2.x. Who can explain that to me please! Matt T.