I think the point is that if the function and design were actually separate, a non functioning element would also be non functioning in plain HTML (no/little design). That would be much easier to spot, and wouldn't even really be the designers problem.

It's understandable why it happens here, the browser can't easily provide this design with pure HTML and CSS, so javascript and SVG are likely carrying some of the load, and bugs there are causing problems.

That said, one of the main benefits of separating function and design is that this stuff isn't supposed to happen, or be much more rare at least, so it is sad that to utilize this we have to introduce those problems again.