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] patch
Sending LayoutTests/ChangeLog Adding LayoutTests/fast/lists/ol-start-parsing.html Adding LayoutTests/platform/mac/fast/lists/ol-start-parsing-expected.checksum Adding (bin) LayoutTests/platform/mac/fast/lists/ol-start-parsing-expected.png Adding LayoutTests/platform/mac/fast/lists/ol-start-parsing-expected.txt Sending WebCore/ChangeLog Sending WebCore/html/HTMLOListElement.cpp Transmitting file data ....... Committed revision 46561. http://trac.webkit.org/changeset/46561