Chris, can you explain more the reason? For now paint invalidation seems to work fine without this bug fixed.

I think the reason was to be able to compute invalidation rects with GeometryMapper for
non-boxes/layers. How is that done without this?

We don't use localBorderBoxProperties, but PaintPropertyTreeBuilderContext, for paint offset and property tree state of the current object, like the following:

    rect.moveBy(FloatPoint(context.treeBuilderContext.current.paintOffset));
    PropertyTreeState currentTreeState(
        context.treeBuilderContext.current.transform,
        context.treeBuilderContext.current.clip,
        context.treeBuilderContext.currentEffect,
        context.treeBuilderContext.current.scroll);

We do need localBorderBoxProperties for paint offset and property tree state of the paint invalidation container which always has localBorderBoxProperties.

Right, thanks for reminding me. Agreed!