Bug 28698 Ctrl+O (show outline) does not work if the file being shown in the editor is read only
M4 The summary tells all. Works if the file is not read only. Is this by design?
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitEditor.java
final char fExitCharacter;
		
		public ExitPolicy(char exitCharacter) {
			fExitCharacter= exitCharacter;
		}
		/*
		 * @see org.eclipse.jdt.internal.ui.text.link.LinkedPositionUI.ExitPolicy#doExit(org.eclipse.jdt.internal.ui.text.link.LinkedPositionManager, org.eclipse.swt.events.VerifyEvent, int, int)
		 */
		public ExitFlags doExit(LinkedPositionManager manager, VerifyEvent event, int offset, int length) {
			
			if (event.character == fExitCharacter) {
				if (manager.anyPositionIncludes(offset, length))
					return new ExitFlags(LinkedPositionUI.COMMIT| LinkedPositionUI.UPDATE_CARET, false);
				else
					return new ExitFlags(LinkedPositionUI.COMMIT, true);
			}	
			
			switch (event.character) {			
			case '\b':
				if (manager.getFirstPosition().length == 0)
					return new ExitFlags(0, false);
				else
					return null;
				
			case '\n':
			case '\r':
				return new ExitFlags(LinkedPositionUI.COMMIT, true);