Hi,
Is it the same behavior when you put the shortcodes in a post (rather than using do_shortcode)?
I don’t know how to see that on your site so I don’t know what you mean by it doesn’t load? You get a blank map? Or no map?
What tab plugin are you using?
I think the problem is that the tabs plugin must itself call do_shortcode() on its content, otherwise it won’t process the inside shortcodes. When I search on Google it seems a lot of people have this problem, for example:
http://wordpress.stackexchange.com/questions/18659/nested-shortcode-doesnt-work
I’m not sure it would work, but maybe you could first explode the map shortcode, then put the result in the tabs? That way they wouldn’t be nested any more:
$tab1 = do_shortcode("[mashup]");
$tab2 = do_shortcode("[mashup]");
echo do_shortcode("[tab name='tab1']$tab1[/tab1]");