CustomWidgetFactory passes wrong arguments to a MultiCheckBoxWidget

I want to use a MultiCheckBoxWidget as a custom widget for a field that is a List with value_type Choice.

In Zope 3.1 this only worked if I subclassed my own widget and made sure that the vocabulary from the value_type was passed.

In Zope 3.2 this should be fixed, but it doesn't work as expected. The widget gets the value_type instead of the value_type's vocabulary passed.

See the following lines in zope/app/form/__init__.py (lines 107ff):

    def __call__(self, context, request):

        # Sequence widget factory
        if ICollection.providedBy(context):
            args = (context, context.value_type, request) + self.args

        # Vocabulary widget factory
        elif IChoice.providedBy(context):
            args = (context, context.vocabulary, request) + self.args

Replacing line 111

            args = (context, context.value_type, request) + self.args

by

            args = (context, context.value_type.vocabulary, request) + self.args

fixes my problem. I don't know if this causes new problems somewhere else.