That explains it: this is a Schabse bug. He reports bugs like: when you have 4 levels of nested generics with an overriden indexed property going through ComImp

That explains it: this is a Schabse bug. He reports bugs like: when you have 4 levels of nested generics with an overriden indexed property going through ComImport, the modopts are incorrectly copied into the method signature, causing a runtime crash in the CLR. It's like having another tester on the C# team :)