If you updated from a version older than 1.0, the option was not existing. So it is possible that your custom post type worked out of the box (because Polylang decided to translate it by default, based on how it was registered) and that now you have to check the option to make it work.
I changed this because the default option was ok for some installations and not ok on some others. The update process from 1.0 or 1.0.1 should not reset this.
