TinyMCE not grabbing content from textarea before hiding that textarea - tinymce

Question

I have an instance of TinyMCE running on a page that enables me to edit existing posts. I query the db, and populate the variable $content with the stored text. I then have the following HTML:
<label for="content">Content:</label>
<textarea name="content" class="post-content" rows="<?php echo $settings_rows; ?>" ><?php echo $content; ?></textarea>
TinyMCE is displaying as an editor, no problem, but is not displaying the text stored in $content. There are no outlying <p> tags, and the $content variable is being populated (I echo'd it outside of the textarea to be sure, and Firebug shows the hidden textarea also being populated).
The editor init is as follows:
tinyMCE.init({
mode : "textareas",
theme : "advanced",
plugins : "advimage",
theme_advanced_buttons1 : "bold,italic,underline,strikethrough,sub,sup,|,justifyleft,justifycenter,justifyright,justifyfull,|,formatselect,fontselect,fontsizeselect",
theme_advanced_buttons2 : "cut,copy,paste,pastetext,|,bullist,numlist,|,outdent,indent,blockquote,|,undo,redo,|,link,unlink,|,image,hr,removeformat,visualaid,charmap,code",
theme_advanced_buttons3 : "",
theme_advanced_toolbar_location : "top",
theme_advanced_toolbar_align : "left",
theme_advanced_resizing : true,
editor_selector : "post-content"
});
Can anyone advise me why this isn't working? I've used it on other pages, using this exact system, without a hitch.
EDIT
As a P.S. the relevant CSS is as follows:
.post-content {
padding: 3px 10px;
width: 90%;
}

Answer 1

Try the following. Give your textarea the id "editor1", use mode: "exact", instead of mode: "textareas",
and initialize your editor the following way (keep the tinymce init where it is for now, but before the following lines)
$(document).ready(function() {
tinyMCE.execCommand('mceAddControl', false, 'editor1');
}

Answer 2

In case someone uses HTML5 and is experiencing TinyMCE behaving similar or as described in the title: Try disabling autocomplete.
<textarea autocomplete="off">Hello, World!</textarea>
If you change/clear the textarea content on the page, your browser will copy those changes every time you reload the page (with autocomplete enabled).
This can make it look as if TinyMCE isn't processing the textarea content.