Separators between TinyMCE buttons -- first one in row shows, but subsequent ones do not

I'm using the TinyMCE Wysiwyg Editor module along with the latest TinyMCE code. The support forum for that module seems to be dead, so I ask here.

In plugin.reg.php, I added two separators in the following line:

$plugins['default']['theme_advanced_buttons1'] = array('bold', 'italic', 'underline', 'strikethrough', 'separator', 'justifyleft', 'justifycenter', 'justifyright', 'justifyfull', 'separator', 'bullist', 'numlist', 'outdent', 'indent', 'undo', 'redo', 'link', 'unlink', 'anchor');

However, there's a problem: Only the first separator displays. This also happens when I add separators between buttons elsewhere.

Is this a bug or something I'm missing about how to have multiple separators in one row?

Thanks,
Steve