It looks like the Binding Editor simply splits the expression at the first dot, without understanding QML. 

Code

import QtQuick

Text {
    id: root
    width: 100
    renderType: Text.NativeRendering
    text: renderType === Text.NativeRendering ? "Native" : "Not Native"
}

Outcome
The Binding Editor treats the binding for root.text as:

• ID: renderType === Text
• Property: NativeRendering ? "Native" : "Not Native"