When setting a breakpoint via "right click" => "Break on subtree modification", the break point is sticky.
Indeed, I tried to desactivate or delete it: it's successfully removed from the Web Inspector interface, but it reappears when I reload the page.
I originally found the bug in the stable version of Chrome. I upgraded to dev channel version, and the bug was still there.
Please tell me if you need any additional information, I would happily provide them.
Created attachment 123580 [details]
Committed r105707: <http://trac.webkit.org/changeset/105707>