HUD: Resizing image annihilates entire aspect ratio.

In my HUD, I have a button which I have set to display an image. When I resize it its entire aspect ratio is destroyed making it look extremely ugly. I have uploaded two pictures down below visualising my problem.

Before resize:

After resize:

To be concise, in the picture you can see that I am resizing a custom widget, which might seem contradictory to my statement that I am resizing a button. The custom widget only contains a button.

I have to come to believe there must be some setting that I can tweak in Unreal Engine but I cannot find any. Or is this possibly a bug?