ArgumentError: options[:field] entry does not map to a property in Model

[postmodern]

While testing ronin-scanners I ran into this error when accessing the ports relationship on IPAddress, which goes through OpenPort.

ip = IPAddress.last
# => #<Ronin::IPAddress: 173.194.33.0>
ip.open_ports
# => [#<Ronin::OpenPort @id=6 @last_scanned_at=2012-09-28 00:00:00 -0700 @created_at=#<DateTime: 2012-09-28T22:26:14-07:00 ((2456200j,19574s,0n),-25200s,2299161j)> @ip_address_id=11 @port_id=2 @service_id=1>, #<Ronin::OpenPort @id=7 @last_scanned_at=2012-09-28 00:00:00 -0700 @created_at=#<DateTime: 2012-09-28T22:26:14-07:00 ((2456200j,19574s,0n),-25200s,2299161j)> @ip_address_id=11 @port_id=1 @service_id=1>]
ip.ports
ArgumentError: +options[:field]+ entry :protocol does not map to a property in Ronin::Port
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:805:in `block in assert_valid_fields'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:796:in `each'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:796:in `assert_valid_fields'
/home/hal/.gem/ruby/1.9.1/gems/dm-aggregates-1.2.0/lib/dm-aggregates/query.rb:23:in `assert_valid_fields_with_operator'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:768:in `block in assert_valid_options'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:766:in `each'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:766:in `assert_valid_options'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/query.rb:363:in `update'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/associations/relationship.rb:158:in `block in query_for'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/repository.rb:114:in `scope'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/associations/relationship.rb:153:in `query_for'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/associations/one_to_many.rb:40:in `collection_for'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/associations/one_to_many.rb:99:in `lazy_load'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/resource/persistence_state/persisted.rb:23:in `lazy_load'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/resource/persistence_state/persisted.rb:8:in `get'
/home/hal/.gem/ruby/1.9.1/gems/dm-core-1.2.0/lib/dm-core/model/relationship.rb:340:in `ports'
(ronin):3:in `start'

I get the same error when calling ip.open_ports.ports and after calling DataMapper.finalize. I have also ran into this error in a Padrino app that also used DataMapper 1.2.0.