Bug 322356 EPS's isPartVisible(MPart) method does not consider placeholders
SSIA
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
((MElementContainer) element).getChildren().add(placeholder);
						}
					} else {
						addToLastContainer(category, providedPart);
					}
				}
			}
		}
		return providedPart;
	}
	private void addToLastContainer(String category, MPart part) {
		MElementContainer<?> lastContainer = getLastContainer();
		MPlaceholder placeholder = part.getCurSharedRef();
		if (placeholder == null) {
			((List) lastContainer.getChildren()).add(part);
		} else {
			((List) lastContainer.getChildren()).add(placeholder);
		}
		if (category != null) {
			lastContainer.getTags().add(category);
		}
	}
	private MElementContainer<?> getLastContainer() {
		MElementContainer<MUIElement> searchRoot = rootContainer;
		List<MUIElement> children = searchRoot.getChildren();
		if (children.size() == 0) {
			MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
			searchRoot.getChildren().add(stack);
			return stack;
		}