1. Create a seam project
2. Create a new folder <project>/NewWebContent
3. Open components.xml with JBT XML Editor
4. Try to edit the file. It works.
5. Open .settings/org.eclipse.wst.common.component
6. Add the new web content folder there:

<wb-resource deploy-path="/" source-path="/NewWebContent">
<wb-resource deploy-path="/" source-path="/WebContent" tag="defaultRootSource"/>

7. Save the file.
8. Try to edit the components.xml againg.
9. It's not working anymore.
10. Close the editor. Open again.
11. Now I can edit it.