[TYPO3-mvc] findBy... not working... seems to return all records

[Stephen Bungert]

$items = $this->itemRepository->findByTags($filterBy['tag']);

Assuming that $filterBy['tag'] is a number , say 3 for example, shouldn't 
the above find all items that have a relation to the tag table record with 
the UID of 3?

It seems to return all items.

The field in the items table is called "tags" and the relations are managed 
by a MM table.

Do I have to make my own repository fundtion for this?

Stephen.