I have a solution for this issue which seems to be working so far.
Edit the plugin and find this section:
echo '<textarea id="multiplecontent_box-'.$fieldName.'" tabindex="2" name="multiplecontent_box-'.$fieldName.'" cols="158" class="theEditor" rows="15">';
$content = get_post_meta($post->ID, '_ot_multiplecontent_box-'.$fieldName , true);
echo apply_filters('the_editor_content', $content);
echo '</textarea>';
Replace it with the following:
wp_editor( get_post_meta($post->ID, '_ot_multiplecontent_box-'.$fieldName , true), 'multiplecontent_box-'.$fieldName, $settings = array() );
Just about that you’ll also see this:
echo '<a id="edButtonHTML" class="hide-if-no-js" onclick="switchEditors.go(\'multiplecontent_box-'.$fieldName.'\', \'html\');">HTML</a><a id="edButtonPreview" class="active hide-if-no-js" onclick="switchEditors.go(\'multiplecontent_box-'.$fieldName.'\', \'tinymce\');">Wysiwyg</a>';
Just comment it out like so:
//echo '<a id="edButtonHTML" class="hide-if-no-js" onclick="switchEditors.go(\'multiplecontent_box-'.$fieldName.'\', \'html\');">HTML</a><a id="edButtonPreview" class="active hide-if-no-js" onclick="switchEditors.go(\'multiplecontent_box-'.$fieldName.'\', \'tinymce\');">Wysiwyg</a>';
This replaces the old style editor with the new editor they’ve introduced in the new version. Again, I haven’t fully tested this implementation yet, but it seems to work for me so far ??