Rules vanish from the rules list

To reproduce it:

• Create two different rules of the same filter.
• Move the second rule you created so it becomes a subrule of the first; you should notice that the rule is now shown indented.
• Click on the save button; the rule is not shown anymore. Even going to a different page, and then returning to the page of the rules associated with the filter, you cannot see the rule anymore (although the rule is still present in the database table).