ServiceHostFactory is not being invoked

I got a ASP.Net hosted service host:

<%@ ServiceHost Language="C#" Debug="true" 
    Service="LongTermStorage.WebService.LongTermStorageService" 
    Factory="LongTermStorage.WebService.SteelServiceHostFactory"
    CodeBehind="LongTermStorageService.svc.cs" %>

SteelServiceHostFactory is not being invoked and I do not get any errors.

Factory:

public class SteelServiceHostFactory : ServiceHostFactory
{
    protected override ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses)
    {
        return new SteelServiceHost(SteelWcfAppli开发者_C百科cation.InstanceProvider, serviceType, baseAddresses);
    }
}

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It works if I switch from Cassini (development web server) to IIS.