not entirely sure why this is happening, but it is being caused by this line at 769:
$CKEditor_config["filebrowserBrowseUrl"] = "webassist/kfm/index.php?uicolor=".urlencode(isset($CKEditor_config["uiColor"])?str_replace("#","%23",$CKEditor_config["uiColor"]):"%23eee")."&theme=webassist_v2&showsidebar=false&startup_folder=".$casepath."/large/";
change that to:
$CKEditor_config["filebrowserBrowseUrl"] = "webassist/kfm/index.php?uicolor=".urlencode(isset($CKEditor_config["uiColor"])?str_replace("#","#",$CKEditor_config["uiColor"]):"#eee")."&theme=webassist_v2&showsidebar=false&startup_folder=".$casepath."/large/";
you will need to save, close and reopen the file, the HTML editors should be editable again.