Hi,
I'm not exactly sure what customization you are talking about as there is no customization for WorkSpaceTabs in the Catalog sample application, it's just standard WorkStpaceTabs control.
I assume you want them to look like this:
If this is not what you get on default theme, then I would advice you to fully clear your cache (including uppering privateversion in web.config and deleting bin and obj folders) and see where that leads you.
Hope this helps,
Palli