Bug 96917 [implementation] If two editors use the 2.x-compatible API, one or both doesn't work
At least one problem is that 3.0 installs partitioners for every editor that might possibly edit a file, but each editor expects its own partitioner to be installed. Leading to the famous white screen with blue line.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitDocumentProvider.java
public void modelChanged(IAnnotationModel model) {
				Object[] listeners= fListenerList.getListeners();
				for (int i= 0; i < listeners.length; i++) {
					((IAnnotationModelListener) listeners[i]).modelChanged(model);
				}
			}
			/**
			 * @see IAnnotationModelListenerExtension#modelChanged(AnnotationModelEvent)
			 */
			public void modelChanged(AnnotationModelEvent event) {
				Object[] listeners= fListenerList.getListeners();
				for (int i= 0; i < listeners.length; i++) {
					Object curr= listeners[i];
					if (curr instanceof IAnnotationModelListenerExtension) {
						((IAnnotationModelListenerExtension) curr).modelChanged(event);
					}
				}
			}
			public void addListener(IAnnotationModelListener listener) {
				fListenerList.add(listener);
			}
			public void removeListener(IAnnotationModelListener listener) {
				fListenerList.remove(listener);
			}
		}
	
	private final static String HANDLE_TEMPORARY_PROBLEMS= PreferenceConstants.EDITOR_EVALUTE_TEMPORARY_PROBLEMS;
	
	private boolean fIsAboutToSave= false;