Qt Quick Software Renderer: Colour changes at fractional coordinates produce a stray black line

The reproducer below uses plain Rectangles. More complex items like Buttons and TabButtons are also affected.

Code

import QtQuick

Window {
    width: 800
    height: 400
    visible: true

    Row {
        padding: 5.5
        spacing: 5.5

        Repeater {
            model: 10
            Rectangle {
                width: 80
                height: 40
                color: ptr.pressed ? "pink" : "silver"

                TapHandler { id: ptr }
            }
        }
    }
}

Steps to reproduce

1. Build and run the code above, using the software renderer
   • linuxfb plugin, OR
   • eglfs plugin + QuickWindow::setGraphicsApi(QSGRendererInterface::GraphicsApi::Software)
2. Click/tap on each of the Rectangles

Outcomes
Everything looks fine at startup. But when a Rectangle changes colour, thin black lines might remain at edges.

The problem does not occur when using hardware rendering (eglfs plugin + OpenGL).