Why are some Siebel objects read only?

I want to add some extensions to an existing Siebel application, but the objects which I need to change remain (partially) read only, despite I have locked the respective parent projects. E.g.

• Add a Menu item to the application main menu. => I can edit existing items, but I cannot add new items开发者_StackOverflow中文版 (Tool's menu "New record" is disabled.)
• Add a custom applet to view "Sales Home Page View". It's read only (Warning displayed by Tools when I click "Edit web layout").

Any ideas, why?

Seems to be a bug in Siebel Tools. After a restart of Tools I was able to perform the desired changes.