In r25065 and below, moving the cursor down in a contentEditable section doesn't work properly if the paragraph has CSS style line-height:1em;. See attached; to reproduce, click in editable area, press the down arrow key.
Created attachment 15979 [details] html file illustrating problem
Confirmed with a local debug build of WebKit r25066 with Safari 3 Public Beta v. 3.0.3 (522.12.1) on Mac OS X 10.4.10 (8R218). This also reproduces on Safari 2.0.4 (419.3) with its original WebKit on 10.4.10, so it's not a regression. Also note the "lip" at the bottom of the <iframe> which bleeds through contents of the iframe! That looks like a different bug, although it's also present on Safari 2.0.4 as well.
Created attachment 15984 [details] Change RenderText hit testing to prefer the lower of two overlapping lines No layout test regressions, but it is perhaps worth mentioning that a more local fix is possible by patching nextLinePosition() to pass a lower y coordinate to positionForCoordinates().
Comment on attachment 15984 [details] Change RenderText hit testing to prefer the lower of two overlapping lines r=me
Landed in r25235.
<rdar://problem/5437710>