Cannot focus on buttons

[Donaldini]

I think the tabIndexes were changed to -1 because of this item #46.

This makes it now impossible to tab on the next and back buttons. Was there a reason to add this?
I can no longer go through the form using only keyboard.

[cristijora]

Actually it is possible to focus on buttons
https://codesandbox.io/s/98j2m8ool4
It works with tab key.