When I look at the SVG code in firebug, it looks like the paths are ok, but that the stroke-width, stroke-color and stroke-dasharray are not.
[ATTACH=CONFIG]14053[/ATTACH]
Compared to the layer made up of paths based on SimpleFillSymbol in the mxd, which are ok:
[ATTACH=CONFIG]14054[/ATTACH]
Note that in my first comment, I said SimpleLineSymbol was displaying ok, which is incorrect, I meant to say SimpleFillSymbol was displaying ok. All line symbols I tried, including SimpleLineSymbol, suffer from this issue.