When using a gamepad (Tested with an X-box 360 Controller) if you press and hold a UMG button down and then use the D-pad or another form of movement the currently pressed widget component (In the test case, a button) loses focus and another widget can get focus. If you click and hold with a mouse the widget component does not lose focus.
This issue occurs in 4.14.3, 4.15.3, and 4.16 binary versions of the engine.
Reproducing this issue requires a Gamepad Controller
Result: The focus changes to another button and activates it
Expected result: Like the mouse the focus should remain on the button that was first pressed.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-45405 in the post.