Have a look at the XML version of the quilt (that little switch on the top right), some components come with XML attributes for configuration, I don't know by heart if message-list is one of them, but I could imagine. The quilt should be ForumPage. Then copy the component code with attributes from the quilt XML and insert an @ when you include it in FreeMarker, does that change anything?
Second factor could, as you already stated, be the CSS, the context in particular. Check the wrapper structure & classnames of the original page. Maybe you have to replicate that outer div structure in your tabbed component so the default styles are properly applied.
