Structuremap instancescope

Question

I have an configuration as follows:

ForRequestedType<ISomeInterface>().CacheBy(InstanceScope.PerRequest)
    .TheDefault.Is.ConstructedBy(x=>x.CacheManager.GetSomeInterface<TestSomeInterface>());

in an ASP.NET application

When I look at ObjectFactory.WhatDoIHave(), it tells me:

ISomeInterface (Namespace.ISomeInterface)
Scoped as : HybridHttpSession

When I set a breakpoint inside the function GetSomeInterface, it only passes once, while it should pass every time I request an SomeInterface, since I explicitly tell structuremap to cache by InstanceScope.PerRequest.

Anyone has an explanation or idea what I am doing wrong?