When making a dump with --dump-slave option, upon completion mysqldump starts slave threads even if they were not stopped by mysqldump itself. This behavior breaks delayed/manually synchronized slaves which have not to be running all the time. Please consider implementing additional check(s) for that, like in the attached patch.

P.S. The comment /* if SLAVE SQL is not running, we don't start it */ in do_start_slave_sql() is opposite and misleading.