I'd say S3, since it would really become an issue in a single-pixel band with few-pixels thin clickable elements, which hopefully aren't that common in the wild. Though, it clearly does affect tests, so I'll look at fixes sooner than later.
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I'd say S3, since it would really become an issue in a single-pixel band with few-pixels thin clickable elements, which hopefully aren't that common in the wild (You could argue that block-in-inline as used in the testcase causes this as well, but users in general wouldn't end up clicking on the zero-height bounding box like the testcase does). Though, it clearly does affect tests, so I'll look at fixes sooner than later.