class MyObject
    {
        public string MyObjectString;
    }
    class MyClass
    {
        private readonly List<MyObject> _items = new List<MyObject>
        {
                new MyObject {MyObjectString = "ItemA"},
                new MyObject {MyObjectString = "ItemB"},
                new MyObject {MyObjectString = "ItemC"}
        };
        private void MyMethod(string suffix)
        {
            foreach (MyObject o in _items)
            {
                o.MyObjectString += suffix; // CC0039 fires on this line
                o.MyObjectString = o.MyObjectString + suffix; // but not on this one
            }
        }
    }