Я решил это. Перед вызовом метода JHTMLArea для textarea сначала скопируйте значение в textarea, а затем примените функцию htmlarea.
$("#txtNotes").val($('#hdnNotesDescription').val());
$("#txtNotes").htmlarea(
{
// Override/Specify the Toolbar buttons to show
toolbar: ["bold", "italic", "underline", "link", "unlink", "orderedlist", "unorderedlist", "indent", "outdent", "justifyleft", "justifycenter", "justifyright"],
toolbarText: $.extend({}, jHtmlArea.defaultOptions.toolbarText,
{
"bold": "Bold",
"italic": "Italic",
"underline": "Under Line",
"link": "Hyperlink",
"unlink": "Remove Hyperlink",
"orderedlist": "Numbering",
"unorderedlist": "Bullets",
"indent": "Increase Indent",
"outdent": "Decrease Indent",
"justifyleft": "Align Text Left",
"justifycenter": "Center",
"justifyright": "Align Text Right"
}),
loaded:function(){
}
});