Using a @2x image with BorderImage displays incorrectly on 5.12.0

On Qt 5.11.2, I could use a HiDPI (2x) image on a BorderImage, and it would scale exactly how I would expect it to. On 5.12.0, this isn't the case. Instead, the bottom segment of the image scales correctly, but the top segment appears to be really squished on both the left and the right side. I've tried many combinations of "source" and "border" properties on the BorderImage element, and I've built my software on different operating systems, but this problem still persists. Standard DPI (1x) images aren't affected by this bug.

I currently can only use Qt 5.11.2 for my software, because I rely on pre-rendered nine-patch BorderImages for many custom controls I've made. Using only standard DPI images isn't an option, because my controls would then look pixelated on HiDPI displays.

Check the attachments for an example of this problem with an image I'm using for the background of buttons.

It's worth noting that this can be worked around by using a ShaderEffect and BorderImageMesh in front of an Image element, with the "size" property set manually to the size of the standard DPI variant of the image. Using three elements shouldn't be necessary to get this working on 5.12.0 though, and I previously didn't have to specify the image's size manually. Here's the code I'm using temporarily for 5.12.0 projects.

Item {
	id: prerenderedImage
	
	property size size
	property string source
	property real topInset: 0
	property real leftInset: 0
	property real bottomInset: 0
	property real rightInset: 0
	
	Image {
		id: image
		
		smooth: false
		source: prerenderedImage.source
		visible: false
		
		anchors.fill: parent
	}
	
	ShaderEffect {
		property var source: image
		
		mesh: BorderImageMesh {
			border {
				top: prerenderedImage.topInset
				left: prerenderedImage.leftInset
				bottom: prerenderedImage.bottomInset
				right: prerenderedImage.rightInset
			}
			
			size: prerenderedImage.size
		}
		
		anchors.fill: parent
	}
}