Currently when calling touch without passing a field, all attributes on the model persist.

This seems to happen on all versions of Mongo.

Example:
person = Person.new(name: 'Fred', updated_at: Time.now)
person.name = 'Bob'
person.touch
person.reload
person.name

Related To Old Fix Attempt (2012):
https://github.com/mongodb/mongoid/commit/796d4e1717f4383de3b4d3eedf1b922863d7b80e