Add/remove user controls programaticaly to placeholder

Question

I make one asp.net web forms app, I create user control, in this user control I insert few standard .net controls. Now in my page.aspx I want dynamicly to insert this user control. I put a button, something like "Add new control".
If I click on it I'm adding a new control to the page. And all this works fine.

I have a problem in removing of this controls. I write a function for removing. But first time when I click it doesn't remove the control, I have to click another time to remove the last control. I think is something with postback, don't know why at first post back it doesn't remove the control.

I'm addding programaticly controls to PlaceHolder which is inside UpdaPanel. Here is the c# code how i do this, pls anybody knows where i make mistake?

 

public partial class Clasess_And_Events : System.Web.UI.Page
{
    protected int NumberControlsForCategory
    {
        get { return (int)ViewState["NumControlsForCategory"]; }
        set { ViewState["NumControlsForCategory"] = value; }
    }


    protected void Page_Load(object sender, EventArgs e)
    {

        if (!IsPostBack)
        {
            //Initiate the counter of dynamically added controls
            this.NumberControlsForCategory = 0;

        }
        else
        {
                //Controls must be repeatedly be created on postback
                this.createControlsCategory();

        }



    }

    private void createControlsCategory()
    {
        int count = this.NumberControlsForCategory;

        for (int i = 0; i < count; i++)
        {


            Control myUserControl = (Control)Page.LoadControl("UserControls/CategoryDropdown.ascx");
            myUserControl.ID = "CategoryControl_ID_" + i.ToString();


            PlaceHolder1.Controls.Add(myUserControl);
        }
    }




    protected void Add_Controll_Click(object sender, EventArgs e)
    {


        Control myUserControl = (Control)Page.LoadControl("UserControls/CategoryDropdown.ascx");
        myUserControl.ID = "CategoryControl_ID_" + NumberControlsForCategory.ToString();


        PlaceHolder1.Controls.Add(myUserControl);

        this.NumberControlsForCategory++;

        LinkButton10.Visible = true;
    }




    protected void Remove_Control_Click(object sender, EventArgs e)
    {

                Control myUserControl = (Control)Page.FindControl("CategoryControl_ID_" + NumberControlsForCategory.ToString());
                PlaceHolder1.Controls.Remove(myUserControl);
                this.NumberControlsForCategory--;
    }
}