I've noticed that the hosting_site.form.js is replacing field descriptions when a field has only one valid value with the text of the only value. This is fine until a hook_form_alter is altering the field reducing it to one value only. In this specific case the current code
$desc_id.show() .find('div.placeholder') .contents(). replaceWith($.trim($input_id.val()));
when contents() method is call it returns an empty element. Replacing it like this example
$desc_id.show() .find('div.placeholder') .html($.trim($input_id.val()));
solves the problem.
Moreover contents() method (similar to children()) is used to fetch the element nodes of the given element. In this context is quite useless because we're trying to fetch nodes and then wipe them out with the replaceWith() call.