Hey, I found the problem. The editor was contained in this structure:
<table>
<form>
<tr><td><editorControl></td></tr>
</form>
</table>
In Netscape and FireFox, the Editor Control will not post back correctly although getHTML shows the correct content. In IE, it works fine.
The reason it was in this odd structure was to remove IE's vertical spacing after a FORM element. I changed the structure below and now everything works:
<form style="margin: 0">
<table>
<tr><td><editorControl></td></tr>
</table>
</form>