Selection highlights of lines in adjoining blocks can overlap
For example, if the selection spans the last line of one block and the first line of the next block, and those lines overlap (due to margins or line-height), the selection highlights will overlap.
<div>first line</div><div style="margin-top: -1ex;">second line</div>
Created attachment 138157 [details]
Use an adjusted selection top for highlighting when the last line in the preceding block is selected and overlaps
Fixed in <http://trac.webkit.org/r114784>.