Created attachment 58415 [details]
Example of the failure
According to http://www.w3.org/TR/SVG/implnote.html#ArcImplementationNotes F.6.6 if either radius is 0 in an arc segment, the arc should be rendered as a line to x,y. WebKit browsers (WebKit nightly, Safari 5 and Chrome 5.0.396) all fail to render anything.
This works in trunk, Dirk confirmed it.