Vaadin tabs with custom content

I have a Vaadin tab component with custom content. In some tabs are buttons insted of simple text. When I navigate the tab component with the keyboard, I can navigate the tabs with the arrow keys.

When I want to activate the button inside a tab, I need to press the tab key again to set the tabindex from the tab to the button.

How can I activate the button with the keyboard navigation without pushing the tab key twice?

In the vaadin tab demo, there is an example of a tab with custom content. Instead of a button, there is a checkbox in a tab but the probleme is the same.