Retainer box fails to render child widgets reliably in 4.26

Development Programming & Scripting UI
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4

I ran into a similar issue where child widgets under a retainer (mostly text based) were not rendering correctly in 4.26. We use source, so not sure how much help this is, but I narrowed it down to the following change:

int32 SRetainerWidget::PaintSlowPath(const FSlateInvalidationContext& Context)
{
	FGeometry OriginalPaintSpaceGeometry = GetPaintSpaceGeometry();
	FSlateRenderTransform SimplifiedRenderTransform(OriginalPaintSpaceGeometry.GetAccumulatedRenderTransform().GetMatrix().GetScale(), OriginalPaintSpaceGeometry.GetAccumulatedRenderTransform().GetTranslation());
	const FGeometry NewPaintSpaceGeometry = FGeometry::MakeRoot(OriginalPaintSpaceGeometry.GetLocalSize(), FSlateLayoutTransform()).MakeChild(SimplifiedRenderTransform, FVector2D::ZeroVector);
	return SCompoundWidget::OnPaint(*Context.PaintArgs, NewPaintSpaceGeometry, Context.CullingRect, *Context.WindowElementList, Context.IncomingLayerId, Context.WidgetStyle, Context.bParentEnabled);
}

Prior to 4.26 thus function just used the GetPaintSpaceGeometry as the 2nd parameter in OnPaint directly:

int32 SRetainerWidget::PaintSlowPath(const FSlateInvalidationContext& Context)
{
	return SCompoundWidget::OnPaint(*Context.PaintArgs, GetPaintSpaceGeometry(), Context.CullingRect, *Context.WindowElementList, Context.IncomingLayerId, Context.WidgetStyle, Context.bParentEnabled);
}

Returning our code locally to that, has our child widgets displaying correctly and the retainer widget still apply its material correctly.

Would be great to know more information behind the change, to see if this is just a bug or if changing this back has some serious consequences.