I was able to reproduce this issue on our end. I have written up a report ( UE-20777) and I have submitted it to the developers for further consideration. I will provide updates with any pertinent information as it becomes available. Thank you for your time and information.
It seems the hit boxes compared the the actual widgets being shown are rotated 90 degrees. So if I have three buttons stacked on top of eachother I have to move from the lower right to the lower left to highlight them.
I had the same issue on 4.10 in standalone game. I made new blueprint with widget and it worked fine. I had pivot in 0.5 0.5 and rescaled it and it worked too.
having the same problem in 4.9 right now.
Changing the coordinate space from “world” to “screen” on the actor’s widget component works nice. So i think it might be a problem with the screenToWorld/worldToScreen projection of either the input or the event area of the widgets.