this seams to be a bug on adding the doctype to the HTML Editor instance.
the issue is c aused by the forward slash before the !:
$CKEditor_config["docType"] = "<\!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">";
should be:
$CKEditor_config["docType"] = "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">";
I have logged this in our bug base.