Just to update you all, it appears that overriding the ucs' "Text" property was the cause of my problem, I changed my property declaration from

public override string Text

to

public string xText

and obviously renamed all the references to "Text", and the "get" was correctly called only once, does anyone know why this should happen ? the functional code for the uc is shown below

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;

namespace CMSUserControls
{
    public partial class CMSUpdateDateTextBox : UserControl
    {
        public CMSUpdateDateTextBox()
        {
            InitializeComponent();
            this.xText = null;
        }

        private void btnUpdate_Click(object sender, EventArgs e)
        {
            this.xText = DateTime.Now.ToString("dd-MM-yy");
        }

        public string xText
        {
            get
            {
                DateTime dt;
                string s = null;
                try
                {
                    dt = DateTime.Parse(this.dtPicker.Text);
                    s = dt.ToString("yyyyMMdd");
                }
                catch
                {
                }
                return s;
            }
            set
            {
                this.dtPicker.Text = value;
            }
        }
   }
}