Strange Slate Border Behavior

I’m trying to create a slate border in which only the bottom margin is used (to create an underline effect for some text). Unfortunately I’m getting some weird behavior in which the border is periodically broken up creating an odd dashed line effect. Where the breaks occur seems dependent on screen width (resize the viewport window and they will move around). The effect also appears in standalone game mode, or when deploying to an Android device, so it is not specific to the editor.

Relevant slate code:

SAssignNew(container, SBorder)
.BorderImage(BridgeUI->GetBrush(FName("Border_Underline_Heavy_Brush")))
[
	hbox.ToSharedRef()
];

I think the setting you want on the brush is actually Box instead of Border. The Border setting will cause things to tile and the Box will cause things to stretch.

That’s my first guess. Please let me know if that helps.