Regression: Type QQmlBinding property State.when fails to accept assignments

Run attached QML code example.

Expected result: When timer triggers property when evaluates to true, state "black" is activated.

Actual result: Property when evaluates to false, and the execution results in following errors:

file:///.../state_bug.qml:23:15: Unable to assign bool to [unknown property type]
file:///.../state_bug.qml:23:15: Unable to assign QQuickRectangle_QML_0 to [unknown property type]