Lambda problem I can not seem to figure out.

Question

I really have no idea how to figure this out, please help. 

 

I have this filter button that is suppose to filter a listbox based on what is filled in a textbox and a list that is used to add the names the listbox

 

this is my code:

public void FilterButton_Click(object sender, RoutedEventArgs e)
        {

//2 filter examples I used

bool Agemin = int.TryParse(AgeBoxMin.Text, out int AgeMi);

//first filter
 if (Agemin && AgeBoxMin.Text.Length != 0 && (AgeBoxMax.Text.Length == 0 || Agemax != true))
            {
                filtercount++;
                int T = 0; while (T < AgeListNumb.Count)
                {
                    if (AgeListNumb[T] > AgeMi)
                    {
                        IndexAge.Add(T);
                        TotalFilter.Add(T);
                    }T++;}}
//second filter
if (JobTextBox.Text.Length != 0)
            {      filtercount++;
                int P = 0; while (P < JobList1.Count)
                {  if (JobList1[P].ToLower().Contains(JobTextBox.Text.ToLower()))
                    {
                        IndexJob.Add(P);
                        TotalFilter.Add(P);
                    }P++;}}

// the filter system:  (probable the problem)
var  matches = TotalFilter.GroupBy(x => x).Where(x => x.Count() == filtercount).Select(x => x.Key).ToList();


// applying filter to Listbox
if (filtercount != 0 && matches.Any())
            {
                AccountNamesList.Items.Clear();

                foreach (var I in matches)
                    AccountNamesList.Items.Add(Listboxlist[I]);
            }

//(Listboxlist contains random names, those names are created with a function)

}

 The first time i run it it runs perfect just as i want it,

But the second time i use the above code it doubles  matches

 

I have looked up what happend with the matches list:

messageBox.Show(Matches.Aggregate("Matches indexes : ", (s1, s2) => s1 + " , " + s2);

If i use the first filter and i allow all items in Listboxlist

to pass( filling in 0 in AgeBoxMin(textbox))

it gives the output:

 

(If listboxlist would contain 6 items )

1,2,3,4,5,6  

 

If i do it again 

I get the output: 1,2,3,4,5,6,7,8,9,10,11,12

 

for some reason it doubles it and makes the entire program crash

because list box only contains 6 items not 12.

 

Maybe somehow it stores all the items in  "var matches" and adds it all up.