Hi @njs
I’m not sure wether this is ACF or WP Core “fault”.
Pretty sure that the ACF wysiwyg-field makes use of the wp_editor function provided by WordPress to output an editor (like any other plugin usually do):
https://codex.wordpress.org/Function_Reference/wp_editor
And it does not seem to have a setting for this. So my guess is that WP Core doesn’t support the same behaviour for editors created with that function as the core editor.
Have you looked into it any further, done some googling on editors in WP in general?
