Binding element when used internally to a component overrides external bindings

I have a Slider in QML that uses two Binding objects inside it. These objects ensure that the Handle follows the "value" property and vice-versa.

In other words, I want my Slider to be usable both as an INPUT widget (user drags slider, value changes) and as an OUTPUT widget (application sets value, user sees the handle in a new position).

See attached example.

To reproduce:
1) Run example (qmlviewer main.qml)
2) Drag slider at the top

=== EXPECTED result ===
a. Bottom slider follows top slider
b. Values of both sliders change as stated by the debug text at the very bottom

=== ACTUAL result ===
(a) does not happen. Bottom slider does not follow the new value set to it.

I understand this is a loop situation, "s2.value" is being affected by two bindings:

1) Binding object internal to S2
2) binding expression written in main.qml (value: s1.value)

However since these bindings converge, I would expect that to work. If it doesn't, is the only solution to properly implement such widget to do that in C++ or use onChanged() imperative event handlers?