Attached is a test HTML document consisting of two divs. The first div is floated left and has 100% width. The second div is editable and has line height 1. After clicking on the editable content, the text insertion cursor appears at the beginning of the editable content but cannot be moved. Text appears to be inserted in the correct location, though, and text can be highlighted as expected. The issue appears to affect the text cursor only. If the first div's width is reduced (to 10%, for example), so that the second div is on the same line as the first, the text cursor behaves as expected. Also, if the line height of the second div is greater than or equal to 1.0625 = 1+1/16, the text cursor behaves as expected. I have verified that this issue appears in Safari 533.5+. This issue does not appear to be present in Firefox 3.6.3. This issue may be related to (or even a duplicate of) bug #26635.
Created attachment 53126 [details] Test document
This issue appears to have been fixed in r58209.