[Mono-list] HashSet does not preserve add order

[Andrus]

Code below produces different results in MONO and .NET .
How to fix ?

Andrus.

using System.Collections.Generic;
using System.Windows.Forms;

class AppMainEntry
{
    static void Main()
    {
        HashSet<string> propList = new HashSet<string>();
        propList.Add("valkogus");
        propList.Add("toode");

        string s = "";
        foreach ( var r in propList )
        {
            s += r + ",";
        }
        // Observed: toode,valkogus,
        // Expected: valkogus,toode,
        MessageBox.Show(s);
    }
}