Is there really multiple iterations of an IEnumerable in this code?

    public static IEnumerable<T> ForEach<T>(this IEnumerable<T> source, Action<T> action)
    {
        foreach (var element in source) action(element);
        return source;
    }

The code above gives me a warning that source is potentially iterated multiple times, but is it really? It's iterated once in the foreach statement, but how does the return statement make it iterated again?