Bug 304211 StackRenderer does not set eagerly created controls to the item
Right-clicking on a Java element and then using 'Open Declaration' opens an editor on the specified file but its content is not shown. Switching tabs or selecting items in the 'Outline' view does _not_ help. Seems to be calling IWorkbenchPage's APIs properly. No idea yet as to what's going on over here.
bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/workbench/ui/renderers/swt/StackRenderer.java
CTabItem[] items = ctf.getItems();
				for (int i = 0; i < items.length; i++) {
					stylingEngine.setClassname(items[i], cssClassName);
				}
				return true;
			}
		};
		ctf.addDisposeListener(new DisposeListener() {
			public void widgetDisposed(DisposeEvent e) {
				updateActiveTab.participating = false;
				folderContext.set(FOLDER_DISPOSED, Boolean.TRUE);
			}
		});
		folderContext.runAndTrack(updateActiveTab, null);
		return newWidget;
	}
	protected void createTab(MElementContainer<MUIElement> stack,
			MUIElement part) {
		MUILabel itemPart = (MUILabel) part;
		CTabFolder ctf = (CTabFolder) stack.getWidget();
		CTabItem cti = findItemForPart(part);
		if (cti != null)
			return;
		int createFlags = SWT.NONE;
		if (part instanceof MPart && ((MPart) part).isCloseable()) {
			createFlags |= SWT.CLOSE;
		}
		
		int index = calcIndexFor(stack, part);
		cti = new CTabItem(ctf, createFlags, index);