If a library class, say, javax.swing.JButton, is being selected from the Projects view, its properties, as displayed by
the Properties view:

1. are few (Modifiers, Name, Extends, Implements);
2. have their values read-only (sure, this is a library class!).

If one opens the same library class in a source code editor and selects "JButton" there, the Properties view will
display a list of properties which are suitable for a user's class (which can undergo refactoring, etc.) -- this list
allows the following class attributes being edited:

1. modifiers;
2. superclass;
3. superinterfaces;
4. javadoc comment.

This is not a harmful yet very annoying behaviour.

The same issue can be observed if a library class name is selected anywhere in the non-read-only source  code (say, one
may have a user class which "extends JButton" or just a code which imports javax.swing.JButton, etc.)