Hi Anton,
What exactly doesn't work? There are some points I noticed:
1) Your LLBLGen version is quite old. The actual Designer build for v3.1 is March 12th, 2012. The RTL is 3.1.12.1015. So, update to the latest version and regenerate again.
2) You don't need to add the inheritance relations as they are added implicitly.
3) I downloaded your repro solution, restored the db backup, opened the LLBLGen project and regenerate code, then I fixed some references and remove the relations to superTypes, then I run the test. I got 152 records from the result. So, it works.
4) I fixed the references on your PrefetchTest.csproj as you were pointing to v3.5 assemblies instead of v3.1. Maybe that's the problem. Here is the part of your vsnet project with the wrong references:
<Reference Include="SD.LLBLGen.Pro.DQE.SqlServer.NET20, Version=3.5.0.0, Culture=neutral, PublicKeyToken=ca73b74ba4e3ff27, processorArchitecture=MSIL">
<SpecificVersion>False</SpecificVersion>
<HintPath>..\..\..\..\..\Intelex.NET\03-System\Lib\SD.LLBLGen.Pro.DQE.SqlServer.NET20.dll</HintPath>
</Reference>
<Reference Include="SD.LLBLGen.Pro.ORMSupportClasses.NET20, Version=3.5.0.0, Culture=neutral, PublicKeyToken=ca73b74ba4e3ff27, processorArchitecture=MSIL">
<SpecificVersion>False</SpecificVersion>
<HintPath>..\..\..\..\..\Intelex.NET\03-System\Lib\SD.LLBLGen.Pro.ORMSupportClasses.NET20.dll</HintPath>
</Reference>
Also, at your PrefetchTest.csproj, you don't need to add reference to SD.LLBLGen.Pro.DQE.SqlServer.NET20. You just need ORMSupportClasses and LinqSupportClasses (if you will make Linq2LLBL queries).
Hope that helps