1, the css standard says: "when the 'border-image-repeat' set as 'round', the image is tiled (repeated) to fill the area. If it does not fill the area with a whole number of tiles, the image is rescaled so that it does. " standard link: http://dev.w3.org/csswg/css3-background/#the-border-image-repeat 2, in webkit implementation doesn't honor what spec said, it just repeat without rescaling. 3, test case is attached.
Created attachment 169791 [details] test case for this bug
Support for round and space was implemented in: https://bugs.webkit.org/show_bug.cgi?id=14185
Someone with the rights could close the issue as resolved?
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.