Qt 5.3:

import QtQuick 2.2
import GSettings 1.0

Window {
GSettings

{id: panelSettings; schema.id: "org.qmldesktop.qmlpanel"; schema.path: "/org/qmldesktop/qmlpanel/"; }

}

completely fails with:
IDs must contain only letters, numbers, and underscores

put // in front of schema.id and it doesn't give the same error but without
setting the schema.id it doesn't do anything.

It seems Qt 5.3 interprets GSettings schema.id the same way id treats it's own id: parameter