i meet a strange bug.
can not find in children class on mongoid 4.0.0 beta

Post < Page

2.0.0p353 :018 > p = Post.new
=> #<Post _id: 52f535d66464682d11010000, created_at: nil, updated_at: nil, title: nil, content: nil, status: nil, published_at: nil, visits: 0, _type: "Post">
2.0.0p353 :019 > p.title = '1'
=> "1"
2.0.0p353 :020 > p.content = '2'
=> "2"
2.0.0p353 :021 > p.save
=> true
2.0.0p353 :022 > Post.first
=> nil
2.0.0p353 :023 > Page.first
=> #<Post _id: 52f535d66464682d11010000, created_at: 2014-02-07 19:37:03 UTC, updated_at: 2014-02-07 19:37:03 UTC, title: "1", content: "2", status: nil, published_at: nil, visits: 0, _type: "Post">
2.0.0p353 :024 >

there is not this bug on mongoid 3.x