File Ownership Changes

I have a shared file on the network whose security properties are changing each time the file is saved. File ownership changes each time a user with modify/change rights saves it. The new owner is the user who last saved a change. Permissions on the file also change when the save is executed. The new permission are inherited from the parent folder. Is this normal behavior? If not, how do I correct it? Other info: This is an NT 4.0 SP6a server. Each file in the folder has diffent permissions.