Why do I find the result repeats after the search?

i use this methode to search for every keyword in textbox1 ind have the result in the listbox2 . But the problem that the results are repeated .

this code used in search button

private void button1_Click(object sender, EventArgs e)
{
// the keyword in text box
string[] pattern = textBox1.Text.Split(new[] { ' ' },StringSplitOptions.RemoveEmptyEntries);
// list_temporare for items in listbox 1
List list_temporare = new List();
// listbox2 for show result
listBox2.Items.Clear();
// add all items in listbox1 in list_temporare (Because linq and lambda does not support the items in the box list or that what I believe)
foreach (DirectoryInfo dr in listBox1.Items)
{
list_temporare.Add(dr);
}
// search for every key word in pattern
var liste_resultat = (from drc in list_temporare
where pattern.All(s => drc.ToString().ToLower().Contains(s.ToLower()))
select drc);
// show result in listbox2
foreach (DirectoryInfo dr in liste_resultat)
{
listBox2.Items.Add(dr);
}
}