Major Description
It happens, when DropDownChoice is enabled, but not enabledInHierarchy (parent container is not enabled).
Every component should update it's rawInput when it's visible and enabled (it means the browser sends it's state in POST).
public final void inputChanged() method should check if the component is enabled on page using
isEnabledInHierarchy() instead of isEnabled().
Otherwise the method resets rawInput value for the component in that case.
Similar situation occures for children of AbstractTextComponent.
The inputChanged() method sets NO_RAW_INPUT value but getValue() method re-reads it's value from the model (and may loose it's temporary value).