Bug 216811 [Markers] ExtendedMarkersView#setFocus doesn't
The result is that focus is lost if you drag the view to another stack... The most common implementation seems to be 'viewer.getControl().setFocus()... To test: select an element in the Problems or Tasks view. Drag the view to a new location (could be in an existing stack or a new one) notice that while the view is the active view the arrow keys don't navigate...
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/ExtendedMarkersView.java
for (int j = 0; j < mementoCategories.length; j++) {
								if (markerCategories[i].getName().equals(
										mementoCategories[j].getID()))
									categoriesToExpand.add(markerCategories[i]
											.getName());
							}
						}
					}
				}
			}
		}
		return categoriesToExpand;
	}
	/**
	 * Restore the expanded categories.
	 * 
	 * @param builder
	 */
	void reexpandCategories(final CachedMarkerBuilder builder) {
		if (!getCategoriesToExpand().isEmpty() && builder.isShowingHierarchy()) {
			MarkerItem[] items = builder.getElements();
			for (int i = 0; i < items.length; i++) {
				String name = ((MarkerCategory) items[i]).getName();
				if (getCategoriesToExpand().contains(name))
					viewer.expandToLevel(items[i], 2);
			}
		}
	}
}