Bug 197113 Project Explorer drag and drop selection not working properly
Create a new java project. Open Project Explorer. Create 2 new classes - Test1 and Test2. Close the java code editors. Select Test1.java in the project explorer. Select Test2.java by doing a mouse down only (so Test1.java still appears highlighted) then drag Test2.java into the code editor area ()- Test1.java is displayed. This only occurs in the Project Explorer, the package explorer works fine.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewer.java
if (contentService != null) {
			contentService.dispose();
		}
		clearSelectionCache();
	}
	/**
	 * Sets this viewer's sorter and triggers refiltering and resorting of this
	 * viewer's element. Passing <code>null</code> turns sorting off.
	 * 
	 * @param sorter
	 *            a viewer sorter, or <code>null</code> if none
	 */
	public void setSorter(ViewerSorter sorter) {
		if (sorter != null && sorter instanceof CommonViewerSorter) {
			((CommonViewerSorter) sorter).setContentService(contentService);
		}
		super.setSorter(sorter);
	}
	/**
	 * <p>
	 * The {@link INavigatorContentService}provides the hook into the framework
	 * to provide content from the various extensions.
	 * </p>
	 * 
	 * @return The {@link INavigatorContentService}that was created when the
	 *         viewer was created.
	 */
	public INavigatorContentService getNavigatorContentService() {
		return contentService;
	}