Bug 336225 Trim bars do not get unrendered by the rendering engine when trimmed window is unrendered
The trim bars are "ignored" by the rendering engine as it does not perform an unrendering pass on them when the parent trimmed window is being unrendered.
bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/PartRenderingEngine.java
if (parentME != null) {
			AbstractPartRenderer renderer = getRendererFor(parentME);
			if (renderer != null) {
				if (!element.isVisible()) {
					parent = getLimboShell();
				} else {
					parent = renderer.getUIContainer(element);
				}
			}
		}
		
		IEclipseContext parentContext = null;
		if (element.getCurSharedRef() != null) {
			MPlaceholder ph = element.getCurSharedRef();
			parentContext = getContext(ph.getParent());
		} else if (parentContext == null && element.getParent() != null) {
			parentContext = getContext(element.getParent());
		} else if (parentContext == null && element.getParent() == null) {
			parentContext = getContext((MElementContainer<MUIElement>) ((EObject) element)
					.eContainer());
		}
		return createGui(element, parent, parentContext);
	}
	private Shell getLimboShell() {
		if (limbo == null) {
			limbo = new Shell(Display.getCurrent(), SWT.NONE);
			limbo.setBackgroundMode(SWT.INHERIT_DEFAULT);
			limbo.setData(ShellActivationListener.DIALOG_IGNORE_KEY,
					Boolean.TRUE);
		}