see attached screenshots.
Created attachment 232480 [details] screenshot1
Created attachment 232481 [details] screenshot2
The second screenshot demonstrates what happens when something gets selected around the broken strikethrough area.
Created attachment 232482 [details] test case
<rdar://problem/17262784>
Created attachment 233844 [details] [PATCH] Fix.
Comment on attachment 233844 [details] [PATCH] Fix. Clearing flags on attachment: 233844 Committed r170456: <http://trac.webkit.org/changeset/170456>
All reviewed patches have been landed. Closing bug.