7.0.0 - Domain objects are automatically inserted when entity is fetched not in a session

[codeconsole]

class User {
     String id 
     static mapping = {
        id generator: 'assigned'
     }
}

def graeme = new User()
graeme.id = 'graeme'
graeme.save(flush:true)

def user = User.get('graeme')
user.save(flush:true, insert:false) // results in BulkWriteError{index=0, code=11000, message='E11000 duplicate key error collection ..

This is caused because there is no common session.

https://github.com/grails/grails-data-mongodb/blob/c8287aadad3777f308ff625096171c24f0eebaf4/grails-datastore-gorm-mongodb/src/main/groovy/org/grails/datastore/mapping/mongo/engine/MongoCodecEntityPersister.groovy#L186-L188

https://github.com/grails/grails-data-mongodb/blob/c8287aadad3777f308ff625096171c24f0eebaf4/grails-datastore-gorm-mongodb/src/main/groovy/org/grails/datastore/mapping/mongo/engine/MongoCodecEntityPersister.groovy#L255-L257

returns false because session.contains(obj) returns false

The following resolves the situation, but it is not intuitive.

User.withSession { 
    def user = User.get('graeme')
    user.save(flush:true, insert:false)
}