I just tested this on WP 4.6 and ACF 5.4.4 and it’s working as expected. I don’t know if there was a bug in the version you were using, but there is nothing mentioned in the readme that a bug related to this has been fixed.
Do you have acf_form_head(); in the template/theme before get_header();
If that’s not it then try deactivating plugins and maybe switching themes to figure out if there is some kind of a conflict.
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