Yootheme loads css that conflicts with Tabs.
In this case mainly this is causing issues:
.nav-stacked {
display: block!important;
}
Using frontend extensions on template frameworks is always a bit of a gamble to see how they play together. In my experience, Yootheme loads a lot of CSS and javascript that potentially clash with other things.
I recommend you ask their support for solutions on this. And/or add your own custom CSS to fix these individual issues.
For more info about how elements get their styling, you can use the Element Inspector of your browser.
When you use YOOtheme, you are able to turn bootstrap off. When I did that, that tabs worked as expected.
Do you think I will have problem with your other products, with bootstrap turned off. I'm not expecting you to respond on a product-by-product basis...but would appreciate your general feedback.