This was caused by trac.webkit.org/changeset/122244 (https://bugs.webkit.org/show_bug.cgi?id=90646)
Created attachment 151673 [details] Screenshot
Created attachment 151674 [details] Reduction This reduction looks different before and after trac.webkit.org/changeset/122244
David, could you please have a look at this? I am not sure which behavior is correct, but I don't think you intended to change it by your patch.
*** This bug has been marked as a duplicate of bug 91000 ***