Receive mails for new questions, but not new answers

I'd like to receive email for every new question, as well as every new answer. My notifications and subscription settings look like this:

• Notify me when: A new question is posted (Instantly)
• Auto subscribe me to: All questions
• On my subscriptions, notify me when: An answer is posted, A comment is posted

I get emails when somebody posts a new question, but I don't receive emails when there are new answers. How do I track down the problem?

I've tracked the problem down so far to this code in forum/subscriptions.py, answer_accepted.py:

subscribers = question.subscribers.filter(
        subscription_settings__enable_notifications=True,
        subscription_settings__notify_accepted=True,
        subscription_settings__subscribed_questions='i'
).exclude(id=action.node.nstate.accepted.by.id).distinct()

The line subscription_settings__subscribed_questions='i' is filtering out the subscribed user. What is the purpose of this code?