Bug 321757 EPS adds a part without considering its placeholder if target container is not a part stack
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
for (MUIElement element : sharedWindow.getSharedElements()) {
				if (element.getElementId().equals(id)) {
					sharedPart = (MPart) element;
					break;
				}
			}
		}
		if (sharedPart == null) {
			MPartDescriptor descriptor = findDescriptor(id);
			sharedPart = createPart(descriptor);
			if (sharedPart == null) {
				return null;
			}
			sharedWindow.getSharedElements().add(sharedPart);
		}
		
		MPlaceholder sharedPartRef = AdvancedFactoryImpl.eINSTANCE.createPlaceholder();
		sharedPartRef.setElementId(sharedPart.getElementId());
		sharedPartRef.setRef(sharedPart);
		return sharedPartRef;
	}
	private MPart addPart(MPart providedPart, MPart localPart) {
		if (providedPart == localPart && isInContainer(providedPart)) {
			return providedPart;
		}
		MPartDescriptor descriptor = findDescriptor(providedPart.getElementId());
		if (descriptor == null) {
			if (providedPart != localPart) {
				MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
				if (providedPart.getCurSharedRef() instanceof MPlaceholder) {