Michi, in questo post del 6 settembre intitolato "Reflection in disagreement with language spec" su MSDN Product Feedback Center, nota lo stesso comportamento segnalato più volte da me qui, qui e qui (e poi anche da Corrado, qui e qui)
Ecco la risposta di Chris (Microsoft), due giorni dopo:
"In general, the language spec does not need to be in agreement with the Type system. Many languages have different type systems which they then map to the CLR type system. The CLR type system is defined in the ECMA specs -- specifically ECMA Partition II specification -- not any specific language spec.
While it's debatable if reflection should return the methods on object when reflecting over an interface -- I could argue either side. However, as we chose to do this in v1.0 the cost of changing that behavior would be breaking some folks and because the benefit is debatable we're not going to commit to making that change."