Clicking on an UMG widget takes the focus for keyboard inputs

  1. Can be focused to false should prevent a button from taking keyboard focus, otherwise there is a bug. Make sure you do this for every button
  2. I know that tab / shift tab has a bug currently in 4.12 where it can result in focusing widgets that do not support keyboard focus. I have reported it already. The best thing is to disable tab + shift tab behavior for now. You can overrule the navigation settings that are defined by default. I did that using the following code:

To register your own behavior have a look at the following classes/methods:

SlateApplication.Get().SetNavigationConfig(MakeShareable(new FNavigationConfig()))) 

i use this method in my gameinstance init

FNavigationConfig → defines if you want to respond to navigation requests when a key is pressed

You simply have to derive from FNavigationConfig and overrule virtual

EUINavigation GetNavigationDirectionFromKey(const FKeyEvent& InKeyEvent) const
{
  return EUINavigation::Invalid;
}

This ensures slate never responds to keyboard navigation requests.