We added this ~3 years ago, and haven't changed it since. I confirmed that reports generated by earlier versions of Lighthouse still present this bug. So the issue is that Chrome / the web changed something, and we must have been relying on some unspec'd behavior. This is a rather complicated SVG so I'm not surprised.

This behavior is visible from every channel: DevTools, PSI, Node.

I see it in Chrome and Firefox, but not Safari.