Hixie recently mentioned this on the whatwg list. IE and the HTML 5 specification both agree that if the start attribute of an ordered list element has a value that can't be parsed, list numbering should start with 1 as if the start attribute was not present at all. Easy to fix.
Created attachment 33742 [details]
Adding (bin) LayoutTests/platform/mac/fast/lists/ol-start-parsing-expected.png
Transmitting file data .......
Committed revision 46561.