This case happened to me when I was using FluentAssertions, when I try to call a C# method that receives the first argument with a default value and a second params argument I can't omit both parameters.

E.g:

    public class Class1
    {
        public static string Foo(string something = "", params object[] args) => 
            string.Format(something, args);
    }

If I try to use this method in F# I expected to be able to call it in this way:

 let result1 = Class1.Foo()

But this gives me an error :

Error FS0501: 
The member or object constructor 'Foo' takes 2 argument(s) but is here given 0. 
The required signature is 'Class1.Foo(?something: string, [<System.ParamArray>] args: obj[]) : string'.

So, to make it work I need to pass the first argument explicitly which I would expect to be optional :

 let result1 = Class1.Foo("")

Pros and Cons

I don't know if this is bt design, but is very confusing and made the interop harder and noisy in some cases.

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