filterbuilder setRetainValuesAcrossFields(false) not working for nested criteria

1.
SmartGWT 4.0
GWT-2.4.0

2. browser(s) and version(s) involved
fire fox 24.7.0


3)
FilterBuilder instance = new FilterBuilder();
instance.setDataSource(xxx);
instance.setRetainValuesAcrossFields(false);

4)
With
setRetainValuesAcrossFields(false) ,
when user changes left side field name, right side user input is cleared.

This works fine unless you click on "+" to add nested filter,
clear action is no longer work.

5)My question if this is a bug, if so, how to clear the value?
Tried using editor on field name, inside its changed
handler, from event we got form, then we got "value" form item, but using clearValue or setValue("") on it, nothing worked.

Please advise.
Thanks a lot!