UMG: Artifacts on box brush mode

Hey there! I have a square UI element which I want to wrap an outline around. I made a 16x16 texture with a 1px border and use that as a brush with Draw As: Box and Margin: 0.25. It works fine, but at certain resolutions or completely at random one of the sides is a little bit smaller. When I zoom in, the problem solves itself, so it’s a little artifact. The first picture shows that. Look at the bottom side of the green ones or at the left side of the blue one. The second picture in the attachment is my texture I use.

Thanks for any help!