Datamapper DataMapper → 0.10.0

I met a weird behavior in associations.

class Foo
  include DataMapper::Resource
  property :id, Serial
  has n, :bars
end

class Bar
  include DataMapper::Resource
  property :id, Serial
  property :value, Integer
  belongs_to :foo
end

DataMapper.auto_migrate!

Foo.create.tap {|foo|
  foo.bars.create(:value => 1)
  foo.bars.create(:value => 1)
}
Foo.create.tap {|foo|
  foo.bars.create(:value => 1)
}

foos = Foo.all
foos.inspect # ???
p foos[1].bars.first(:value => 1)
#=> #<Bar id=1 value=1 foo_id=1>   # expecetd: foo_id=2
p foos[1]
#=> #<Foo id=2>

foos = Foo.all
p foos[1].bars.first(:value => 1)
#=> #<Bar id=3 value=1 foo_id=2>   # correct
p foos[1]
#=> #<Foo id=2>

The result is different when inspect is called.
Is this a known bug?

I'm using dm-core 0.9.11, data_objects 0.9.12 and ruby 1.8.7.