ArgumentException from EntityKey constructor when running a HQL query

I have an object, Prospect, which I am searching for using a Criteria. I set a rather large number of fetch modes on this criter:

DirectCampaignSegment:Join
DirectCampaignSegment.DirectCampaign:Join
DirectCampaignSegment.DirectCampaign.Contract:Join
DirectCampaignSegment.DefaultProgram:Join
Member:Join
Member.Replaces:Join
Member.ACHAccounts:Join

In EntityKey.cs on line 35 I get the following error:

if( !identifierType.ReturnedClass.IsAssignableFrom( id.GetType() ) )
{
throw new ArgumentException( "identifier type mismatch", "id" );
}

At the point the code breaks, 'clazz' is MemberACHAccount. Yet the 'id' value is a valid DirectCampaignSegment id.

exec sp_executesql N'SELECT this_.Prospect_ID as Prospect1_0_7_, this_.Seg_ID as Seg2_0_7_, this_.MemberId as MemberId0_7_, this_.ParticipantId as Particip4_0_7_, this_.OriginalCoverageId as Original5_0_7_, this_.CoverageType as Coverage6_0_7_, this_.CoverageAmount as Coverage7_0_7_, this_.CorrespondenceId as Correspo8_0_7_, this_.InsuredId as InsuredId0_7_, this_.NewCoverageId as NewCove10_0_7_, directcamp2_.Id as Id34_0_, directcamp2_.DirectCampaignId as DirectCa2_34_0_, directcamp2_.DefaultForChannel as DefaultF3_34_0_, directcamp2_.DefaultProgramId as DefaultP4_34_0_, directcamp2_.CorrespondenceId as Correspo5_34_0_, directcamp2_.EffectiveDate as Effectiv6_34_0_, directcamp2_.Name as Name34_0_, directcamp3_.Id as Id31_1_, directcamp3_.ContractId as ContractId31_1_, contract4_.Id as Id29_2_, contract4_.EnrollmentUrl as Enrollme2_29_2_, contract4_.EffectiveDate as Effectiv3_29_2_, contract4_.ExpireDate as ExpireDate29_2_, contract4_.CancelDate as CancelDate29_2_, contract4_.ClientId as ClientId29_2_, contract4_.ProductId as ProductId29_2_, contract4_.ManagingBrokerId as Managing8_29_2_, program5_.Id as Id42_3_, program5_.Name as Name42_3_, program5_.ProgramProfileId as ProgramP3_42_3_, program5_.ContractId as ContractId42_3_, program5_.EffectiveDate as Effectiv5_42_3_, program5_.EndDate as EndDate42_3_, program5_.EnrollmentEndDate as Enrollme7_42_3_, program5_.DescriptionHtml as Descript8_42_3_, program5_.EnrollmentDocumentTemplateStackId as Enrollme9_42_3_, program5_.InformationDocumentTemplateStackId as Informa10_42_3_, program5_.ProcessEnrollments as Process11_42_3_, program5_1_.BasicCoverageAmount as BasicCov2_63_3_, case when program5_1_.Id is not null then 1 when program5_.Id is not null then 0 end as clazz_3_, member6_.Id as Id13_4_, member6_.IntId as IntId13_4_, member6_.ClientId as ClientId13_4_, member6_.FirstName as FirstName13_4_, member6_.MiddleName as MiddleName13_4_, member6_.LastName as LastName13_4_, member6_.Address1 as Address7_13_4_, member6_.Address2 as Address8_13_4_, member6_.City as City13_4_, member6_.StateOrProvince as StateOr10_13_4_, member6_.PostalCode as PostalCode13_4_, member6_.DateOfBirth as DateOfB12_13_4_, member6_.EMailAddress as EMailAd13_13_4_, member6_.CRC32 as CRC14_13_4_, achaccount7_.MemberId as MemberId_9, achaccount7_.Id as Id9_, achaccount7_.Id as Id53_5_, achaccount7_.MemberId as MemberId53_5_, achaccount7_.Type as Type53_5_, achaccount7_.Number as Number53_5_, achaccount7_.TransitRoutingNumber as TransitR5_53_5_, replaces8_.MemberId as MemberId_10, member9_.Id as Original2_10_, member9_.Id as Id13_6_, member9_.IntId as IntId13_6_, member9_.ClientId as ClientId13_6_, member9_.FirstName as FirstName13_6_, member9_.MiddleName as MiddleName13_6_, member9_.LastName as LastName13_6_, member9_.Address1 as Address7_13_6_, member9_.Address2 as Address8_13_6_, member9_.City as City13_6_, member9_.StateOrProvince as StateOr10_13_6_, member9_.PostalCode as PostalCode13_6_, member9_.DateOfBirth as DateOfB12_13_6_, member9_.EMailAddress as EMailAd13_13_6_, member9_.CRC32 as CRC14_13_6_ FROM Prospects this_ left outer join DirectCampaignSegment directcamp2_ on this_.Seg_ID=directcamp2_.Id left outer join DirectCampaign directcamp3_ on directcamp2_.DirectCampaignId=directcamp3_.Id left outer join Contract contract4_ on directcamp3_.ContractId=contract4_.Id left outer join Program program5_ on directcamp2_.DefaultProgramId=program5_.Id left outer join InsurancePlan program5_1_ on program5_.Id=program5_1_.Id left outer join Member member6_ on this_.MemberId=member6_.Id left outer join MemberAccount achaccount7_ on member6_.Id=achaccount7_.MemberId left outer join MemberReplacement replaces8_ on member6_.Id=replaces8_.MemberId left outer join Member member9_ on replaces8_.OriginalMemberId=member9_.Id WHERE this_.CorrespondenceId = @p0', N'@p0 int', @p0 = 1386139

Sorry for the length of that. Notice the second selected field: `this_.Seg_ID as Seg2_0_7_` This is the int which is trying to be used as the <id> However, it's not really the right field! The right field for MemberACHAccount would be `achaccount7_.Id as Id9_` Hmm. I notice that both Id*_ and FieldName_X_Y_ are selected for some things, yet I see no selection for DirectCampaignSegment.Id in that query. Where is it going?

The Seg_ID field is actually the FK for the DirectCampaignSegment relationship (many-to-many). It is somehow getting this confused with the MemberACHAccount Id.