When resizing the HTML editor using the JavaScript functionality provided in Moodle 2.0 it is possible to resize the textarea past the designated space making it difficult to resize without having knowledge of temporary CSS editors (like firebug) or actually editing the CSS and making the icon visible so that you can resize.

Solution: Use JavaScript to prevent resizing over a certain percentage, or change the z-index so the textarea appears above the other content - see http://blog.davglass.com/files/yui/resize3/