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
curTR.dispose();
			if (tb.getSize().y > ctf.getTabHeight())
				ctf.setTabHeight(tb.getSize().y);
			
			
			String cssClassName = (String) ctf
					.getData("org.eclipse.e4.ui.css.CssClassName"); 
			stylingEngine.setClassname(tb, cssClassName);
			ctf.setTopRight(tb, SWT.RIGHT);
			ctf.layout(true);
			
			
			
			
			
			
			
			
			
			ctf.notifyListeners(SWT.Resize, null);
		}
	}
	private ToolBar getToolbar(MUIElement element) {
		if (!(element instanceof MPart))
			return null;
		MPart part = (MPart) element;
		boolean hasMenu = part.getMenus() != null && part.getMenus().size() > 0;
		boolean hasTB = part.getToolbar() != null;
		if (!hasMenu && !hasTB)
			return null;