Bug 303549 [UI] Dragging the last element from a stack causes placeholders to appear
The check to 'pick' a new element to select isn't checking whether the 'toBeRendered' is true.
bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/workbench/ui/renderers/swt/StackRenderer.java
if (!canClose) {
					event.doit = false;
					return;
				}
				part.setToBeRendered(false);
			}
		};
		ctf.addCTabFolder2Listener(closeListener);
		
		
		ctf.addListener(SWT.Activate, new org.eclipse.swt.widgets.Listener() {
			public void handleEvent(org.eclipse.swt.widgets.Event event) {
				CTabFolder ctf = (CTabFolder) event.widget;
				MPartStack stack = (MPartStack) ctf.getData(OWNING_ME);
				MPart part = stack.getSelectedElement();
				if (part != null)
					activate(part);
			}
		});
	}
	private void showTab(MElementContainer<MUIElement> parentElement,
			MUIElement element) {
		CTabFolder ctf = (CTabFolder) getParentWidget(element);
		Control ctrl = (Control) element.getWidget();
		CTabItem cti = findItemForPart(parentElement, element);
		cti.setControl(ctrl);
		ToolBar tb = getToolbar(element);
		if (tb != null) {
			Control curTR = ctf.getTopRight();
			if (curTR != null)