F# issue with byref likes

type IRef = 
    abstract member Ref: unit -> byref<int>

type C() =
    let mutable num = 10
    member _.Get() = num
    member _.Ref() = &num 

    interface IRef with
        member this.Ref() = &this.Ref() 

let inline func (c: C) =
    &c.Ref()

let inline func'<'a when 'a :> IRef> (c: 'a) =
    &c.Ref()

let inline func'' (c: ^c when ^c: (member Ref: unit -> byref<int>)) = // should compile
    &c.Ref() //compile time error FS3236: Cannot take the address of the value returned from the expression. Assign the returned value to a let-bound value before taking the address.

let inline func''' (c) = // should compile
    &(^c: (member Ref: unit -> byref<int>) c) //compile time error FS3236: Cannot take the address of the value returned from the expression. Assign the returned value to a let-bound value before taking the address.

let inline func'''' (c) : byref<int> = // should return `int` instead of `byref<int>` according to https://github.com/fsharp/fslang-design/blob/main/FSharp-4.5/FS-1053-span.md#implicit-dereference-of-return-byrefs
    (^c: (member Ref: unit -> byref<int>) c) //but error on calling - error FS0001: This expression was expected to have type
//    'byref<int>'    
// but here has type
//    'int'    

let g () =
    let c = C()
    let mutable x = &func'''' c
    x <- 1000
    c.Get()