Given two lines of text, one above the other. If a smaller font size and non-transparent background-color is applied to the second line, the second line will overlap the first by some small amount. Note that the first line needs to contain a letter that extends below the bottom of the line (i.e. y, g, j, etc).
1. Go to the midas demo: http://www.mozilla.org/editor/midasdemo/
2. Enter the following HTML:
g<br><span style="background: #f00"><font size="2">g</font></span>
3. Note that the background color of the lower g overlaps the first g.
This reproduces in Chrome 18.104.22.168 but does not reproduce in Safari 4.0.3.
I'm pretty sure this is a dupe of 32495, although the repro cases are slightly different.
It seems like this bug has been resolved. As Julie suggests, this might have been an duplicate of the bug 32495, which has been resolved since http://trac.webkit.org/changeset/53200.