This bug report comes from QuirksMode. When text is shrunken or enlarged in Safari (via Cmd-- or Cmd-+), generated content can cause text to be pushed outside of its bounding box. Example @ http://www.easy-designs.net/articles/safariGeneratedContentWidthBug/
The way this happens with shrinking is that shrinking can cause a wrapped line to unwrap, thus becoming large enough to escape the bounding box.
*** This bug has been marked as a duplicate of 9262 ***