Test script to demonstrate MDL-56800

test-MDL-56800.php

<?php

require_once(__DIR__.'/config.php');
require_once($CFG->libdir . '/formslib.php');

class test_form extends moodleform {
    public function definition() {
        $mform = $this->_form;

        $grp = [];

        for ($j = 0; $j < 4; $j++) {
            $text = 'Text '.$j;
            $value = 'val_'.$j;
            $grp[] = $mform->createElement('radio', 'elname', '', $text, $value);
        }
        $mform->addGroup($grp, 'grpid', '', "<br />\n", false);

        $this->set_data([
            'elname' => 'val_2',
        ]);

    }
}

$PAGE->set_context(context_system::instance());
$PAGE->set_title('test');
$PAGE->set_url('/test-MDL-56800.php');

// Display two forms as non-editable.
$form1 = new test_form(null, null, 'post', '', null, false);
$form2 = new test_form(null, null, 'post', '', null, false);

echo $OUTPUT->header();

echo $OUTPUT->heading('Test 1');
$form1->display();

echo $OUTPUT->heading('Test 2');
$form2->display();

echo $OUTPUT->footer();