Unable to cast transparent proxy to type from AppDomain

Question

I'm trying to create an object in an appdomain:

var type = typeof (CompiledTemplate);
var obj = (CompiledTemplate) domain.CreateInstanceAndUnwrap (
    type.Assembly.FullName, type.FullName);

However, I always get the following error:

Unable to cast transparent proxy to type 'Mono.TextTemplating.CompiledTemplate'.

I'm running on .NET 4.0, not Mono, despite what the namespace might suggest :)

As far as I know, this error happens when .NET thinks that the Type & Assembly do not exactly match in the two domains. However, when debugging, the FullName and Location are identical. Only the Assembly.Codebase property differs - in the child AppDomain its extension is uppercased to "DLL" for some reason.

I've tried adding an AssemblyResolve handler to the AppDomain, which uses Assembly.LoadFrom to load the filename explicitly, but the CodeBase's extension still gets uppercased. Since the original assembly was also loaded with Assembly.LoadFrom (via Mono.Addins), the difference between the CodeBase values seems very strange.

Any suggestions for fixing or working around this problem?