Gem Mongoid: multiples order_by in embbeds_many not work?

Example:
School embeds_many :students

In rails console:

School.first.students.order_by(:name.asc, :email.desc)

Works with name. but why ordering from second field (email) not work?? It’s a bug?

I opened an issue in mongoid gem, but maybe it’s a mongodb problem insted

https://github.com/mongoid/mongoid/issues/3782