how do I control the message box while using the up down control?

I wrote this code to handle the up down control handle it is associated with an edit box and populates a valuelist editor, all I want to do is ask a question if the user presses the down button on the up down control which deletes a row in the valuelist editor if yes delete row if not dont do anything. It seems to work fine but if you answer the question with a cancel then clicking anywhere on the form causes the up down control to be clicked again....Why???

void __fastcall TForm1::UpDown1Click(TObject *Sender, TUDBtnType Button)
{
    //we are clicking up if Button is 0
    if(Button == 0)
    {
        //insert new row with group number
        ValueListEditor2->Strings->Add("Group " + AnsiString(Edit1->Text) + "=");
         //we must be clicking down if Button is 1
      } else {
        //user must press ok for this code to execute
        if(MessageBox(0, (LPSTR)"Do you really want to erase the group?", "ERROR", MB_ICONWARNING | MB_OKCANCEL) == IDOK)
        {
            ValueListEditor2->DeleteRow(ValueListEditor2->RowCount-1);
        //user must have pressed no
        } else {
            Edit1->Text = ValueListEditor2->RowCount-1;
        }
    }
    if(Edit1->Text == "0")
        ValueListEditor2->Visible = false;
    else
        ValueListEditor2->Visible = true;
}