SetKeyboardFocus Stopped Working

FSlateApplication::Get().SetKeyboardFocus(InputField);
stopped working with Unreal Engine 4.15p1.

Steps to reproduce:
1 create a new slate widget with an SEditableTextBox and display it in an editor window.
2. add a button to the widget in order to call the set keyboard focus method
3. Call the SetKeyboardFocus method.
4. focus does not get set

This is happening again in 4.18