TestCase:

import QtQuick 2.1
import QtQuick.Controls 1.0
import QtQuick.Layouts 1.0

RowLayout {
    width: 200
    height: 200
    TextInput {text: "hello" }
}

RowLayout uses the implicit width/height and create connections using implicitWidthChanged from its items. If an Item (like TextInput) is based on QQuickImplicitSizeItem it causes a warning:

Warning:
"QMetaObject::indexOfSignal: signal implicitWidthChanged() from QQuickItem redefined in QQuickImplicitSizeItem"