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
if (document instanceof ISynchronizable && model instanceof ISynchronizable) {
            Object lock= ((ISynchronizable) document).getLockObject();
            ((ISynchronizable) model).setLockObject(lock);
        }
    }
    /*
	 * @see org.eclipse.ui.editors.text.TextFileDocumentProvider#disposeFileInfo(java.lang.Object, org.eclipse.ui.editors.text.TextFileDocumentProvider.FileInfo)
	 */
	protected void disposeFileInfo(Object element, FileInfo info) {
		if (info instanceof CompilationUnitInfo) {
			CompilationUnitInfo cuInfo= (CompilationUnitInfo) info;
			try  {
			    cuInfo.fCopy.discardWorkingCopy();
			} catch (JavaModelException x)  {
			    handleCoreException(x, x.getMessage());
			}
			if (cuInfo.fModel != null)
				cuInfo.fModel.removeAnnotationModelListener(fGlobalAnnotationModelListener);
		}
		super.disposeFileInfo(element, info);
	}
	
	/*
	 * @see org.eclipse.ui.editors.text.TextFileDocumentProvider#connect(java.lang.Object)
	 * @since 3.2
	 */
	public void connect(Object element) throws CoreException {
		super.connect(element);
		if (getFileInfo(element) != null)
			return;