it works as you said for nothing. As this patch got accepted: this behavior is expected, but it is not perfect as we expect to pass `{post: {category: []}}`, but I don't know how to do that.



The case when something is selected: Are you sure?

I would recommend the following workaround anyway: http://stackoverflow.com/questions/8929230/why-is-the-first-element-always-blank-in-my-rails-multi-select-using-an-embedde/8939205#8939205