Bug 68011 [java search] "Search the JRE System Libraries" looks like a local preference but behaves as a global one... [search]
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/actions/FindImplementorsInWorkingSetAction.java
public FindImplementorsInWorkingSetAction(JavaEditor editor) {
		super(editor);
	}
	/**
	 * Note: This constructor is for internal use only. Clients should not call this constructor.
	 * @param editor the Java editor
	 * @param workingSets the working sets to be used in the search
	 */
	public FindImplementorsInWorkingSetAction(JavaEditor editor, IWorkingSet[] workingSets) {
		this(editor);
		fWorkingSets= workingSets;
	}
	void init() {
		setText(SearchMessages.Search_FindImplementorsInWorkingSetAction_label); 
		setToolTipText(SearchMessages.Search_FindImplementorsInWorkingSetAction_tooltip); 
		setImageDescriptor(JavaPluginImages.DESC_OBJS_SEARCH_DECL);
		PlatformUI.getWorkbench().getHelpSystem().setHelp(this, IJavaHelpContextIds.FIND_IMPLEMENTORS_IN_WORKING_SET_ACTION);
	}
	protected JavaSearchQuery createJob(IJavaElement element) throws JavaModelException {
		IWorkingSet[] workingSets= fWorkingSets;
		if (fWorkingSets == null) {
			workingSets= JavaSearchScopeFactory.getInstance().queryWorkingSets();
			if (workingSets == null)
				return null;
		}
		SearchUtil.updateLRUWorkingSets(workingSets);
		return new JavaSearchQuery(new ElementQuerySpecification(element, getLimitTo(), getScope(element), getScopeDescription(element)));
	}
}