CustomCollectionEditor's alwaysCreateNewCollection doesn't work correctly

[daigo]

I'm using SpringMVC 3.0.3.

I store form object to session using @SessionAttribute annotation. I've created my CustomCollectionEditor to turn on alwaysCreateNewCollection, but it doesn't work correctly.

I have one form that has one List<String> like following:

public class FooForm {
  private List<String> bar;

(omit getter/setter)
}

Then I registered my CustomCollectionEditor to my controller:

@Controller
public class SomeController {
  @InitBinder
  protected void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(List.class, new MyCustomCollectionEditor);
  }
(omit)
}

I send post two request.

1st request:
bar[0]=a1
bar[1]=b1
bar[2]=c1

Then FooForm has correct List<String> field(bar[0]=a1, bar[1]=b1, bar[2]=c1).

2nd request:
bar[0]=a2
bar[1]=b2

Then FooForm's bar field has bar[0]=a2, bar[1]=b2, bar[2]=c1.

I want to eliminate bar[2]=c1, so I've create my CustomCollectionEditor.
However BeanWrapperImpl doen't call my CustomCollectionEditor on second request because BeanWrapperImpl can find form object from session. I have no way to change this binding behavior.

I couldn't find any good way other than create custom SesstionAttributeStore to avoid this problem. But I think it is not good way to solve this. Is this bug? Or is there any good way to solve this problem?