fslib | Finite state transducer library | Router library

In general, the C# language will not handle many F# specific features. Most F# types, when used from F#, have different functionality. For example, F# types are (by default) unable to be set to null, but in C#, you can declare and set them to null because the C# language doesn't understand any of the F# specific constructs. As you've discovered, equality and comparison guarantees, nullable guarantees and features, and more are all ignored by C# (and other CLR languages).

In practice, this is rarely a problem, as most people tend to keep the F# types within their F# code base, and pull in types from the BCL or C# projects and convert them to F# types (to add the safety guarantees) "at the API boundaries".