Created attachment 154499 [details]
Test case showing various flex items and unexpected sizes
Column-flow flex items seem to ignore border-box directive for width (and for height in row-flow).
Yeah, we don't work with padding-box either.
Here are the existing bugs filed against flex box: https://bugs.webkit.org/showdependencytree.cgi?id=62048&hide_resolved=1
*** This bug has been marked as a duplicate of bug 70771 ***