Steps to reproduce. 1. Open the attached URL. 2. Place caret/cursor in the second editable paragraph. 3. Press the Format block link. 4. Observe the strange span that got added to the start of block element.
Confirmed with WebKit 525.1+ on Mac OS X 10.5. Thanks for the simple test case!
<rdar://problem/5604313>
I have a fix for this out for review.
Fixed in http://trac.webkit.org/projects/webkit/changeset/32497
*** Bug 21505 has been marked as a duplicate of this bug. ***