Created attachment 460672 [details] the three file default all none column-span have different display in chrome and webkit. It might be a bug. column-span default like all but must default none . default none is from https://developer.mozilla.org/en-US/docs/Web/CSS/column-span. my webkit version is 2.36.0
The tests file do not contain anything useful and are not related to the title..
<rdar://problem/96867250>
Thank you for filing this issue. This looks to be about <details> in a multicolumn content. WebKit (historically) does not handle such content very well :(