I want to create multiple-author blog with different group permissions for different post categories. I think, I managed to do something like that using Role Scoper, but one thing stops me from launching the blog.

When low-level auhor creates new post, (s)he is able to change an author freely. It means that it is possible to write a post in higher-level author name!

I searched all the settings, searched for plug-ins, but without success. I don't know where to go.

Should this issue be solved by disabling change of post author, or by interpreting author changing permissions or similar..?