This is my best solution so far;
//select first tab by default
add_action('acf/input/admin_head', 'my_acf_input_admin_head');
function my_acf_input_admin_head() { ?>
<script type="text/javascript">
jQuery(function($){
$('.acf-tab-group li:first-child a').trigger("click");
});
</script>
<?php }
The old functionality is desirable in many applications.
@enfueggo Did you figure out a way to disable this?