Bug 274236 [CommonNavigator] Incorrect check for existence of item in contribution memory
The check in the NavigatorContentService.rememberContribution() should be containsKey(), not containsValue()
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
* @return The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         either declared through a
	 *         <b>org.eclipse.ui.navigator.viewer/viewerContentBinding</b> to be
	 *         a root element or have a <b>triggerPoints</b> expression that is
	 *         <i>enabled</i> for the given element.
	 */
	public Set findRootContentExtensions(Object anElement,
			boolean toRespectViewerRoots) {
		SortedSet rootExtensions = new TreeSet(
				ExtensionPriorityComparator.INSTANCE);
		if (toRespectViewerRoots
				&& viewerDescriptor.hasOverriddenRootExtensions()) {
			NavigatorContentDescriptor[] descriptors = CONTENT_DESCRIPTOR_REGISTRY
					.getAllContentDescriptors();
			NavigatorContentExtension extension = null;
			for (int i = 0; i < descriptors.length; i++) {
				if (isActive(descriptors[i].getId())
						&& isRootExtension(descriptors[i].getId())) {
					extension = getExtension(descriptors[i]);
					if (!extension.hasLoadingFailed()) {
						rootExtensions.add(extension);
					}
				}
			}
		}
		if (rootExtensions.isEmpty()) {
			return findContentExtensionsByTriggerPoint(anElement);
		}
		return rootExtensions;