Description
In Symfony 2.7 (with choices_as_values set to false) it was possible to have choices in different choice groups that shared the same labels, this is not possible anymore.

Instead of this hack proposed in Symfony Docs, @Tobion wondered in this comment if this use-case be better solved by allowing group_by option to return an array of groups? This way people would just add the choices once and then could add them to multiple groups if needed.