Many-to-many not working with interface

First off, here's a pastie with all the code and mappings involved, and a stacktrace: http://pastie.org/5372087

Not sure if this a bug or not, but I think that according to the docs this should work - in a vendor bundle I have an entity defining a unidirectional many-to-many relation to an interface: the entity is Group and defines a many-to-many relation to a UserInterface, which is resolved correctly in the app configuration (as the many-to-one relations using it in the other entities of this vendor bundle work fine).

I'm going by these docs:

http://symfony.com/doc/master/cookbook/doctrine/resolve_target_entity.html

However, when adding a user to a group, I'm getting a weird error:

An exception occurred while executing 'INSERT INTO acme_group_user (group_id, user_id) VALUES (?, ?)' with params

:

SQLSTATE[HY093]: Invalid parameter number: number of bound variables does not match number of tokens

For some reason it's adding 4 parameters to the statement instead of 2.

Oddly enough, the query generation works perfectly fine when I replace the interface in the mapping with the actual final entity. But that wasn't the point of the exercise... I need to use the interface there.

Also, in other entities in that GroupBundle which are referencing the UserInterface using a different relation type, i.e. many-to-one, the relations work perfectly fine.

The schema validates as well, using doctrine:schema:validate in the console.