Bug 321755 EPS adds a part without considering its placeholder if no target container or part stacks could be found
The summary probably makes no sense. Will deliver a fix with a test in a bit.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
}
				}
			}
		}
		return providedPart;
	}
	private void addToLastContainer(String category, MPart part) {
		MElementContainer<?> lastContainer = getLastContainer();
		if (lastContainer instanceof MPartStack) {
			MPartStack stack = (MPartStack) lastContainer;
			if (part.getCurSharedRef() instanceof MPlaceholder) {
				stack.getChildren().add(part.getCurSharedRef());
			} else {
				stack.getChildren().add(part);
			}
		} else {
			((List) lastContainer.getChildren()).add(part);
		}
		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;
		}