Why isn't this concept working as I would expect?

[dawkot]

    type
        ConceptA = concept c
        
        ConceptB = concept c
            c.myProc(x: ConceptA)
        
        Obj = object
    
    proc myProc(obj: Obj, x: ConceptA) = discard
    
    echo Obj is ConceptB #expected true, returns false