listview items disappearing

So.. my listview items are disappearing after they're scrolled off the screen. They're there, you scoll down, back up, and they're gone. After rotation they reappear, but I have no idea why this is happening.

package com.teslaprime.prirt;

import android.app.Activity;
import android.os.Bundle;
import android.content.Intent;
import android.content.Context;
import android.content.ContentValues;
import android.view.View;
import android.view.ViewGroup;
import android.view.LayoutInflater;
import android.widget.CheckBox;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.TextView;
import android.widget.ListView;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.Cursor;
import java.util.ArrayList;
import java.util.List;
import java.util.Date;

public class TaskList extends Activity {
  List<Task> tasks = new ArrayList<Task>();
  TaskAdapter adapter = null;
  SQLiteDatabase db = null;

  public void populateList(){
      adapter = new TaskAdapter();
      adapter.clear();
      Cursor cur = db.query("tasks",null,null,null,null,null,"timestamp");
      cur.moveToFirst();
      int anchor = 0;
      while (cur.isAfterLast() == false) {
        if (cur.getInt(cur.getColumnIndex("completed")) == 1) {
            Task task = new Task(cur.getString(cur.getColumnIndex("name")),cur.getString(cur.getColumnIndex("type")));
            task.id = cur.getInt(cur.getColumnIndex("id"));
            task.completed = 1;
            adapter.add(task);
            anchor = anchor+1;
        }
          cur.moveToNext();
      }
      cur.moveToFirst();
      while (cur.isAfterLast() == false) {
          if (cur.getInt(cur.getColumnIndex("completed")) == 0) {
              Task task = new Task(cur.getString(cur.getColumnIndex("name")),cur.getString(cur.getColumnIndex("type")));
              task.id = cur.getInt(cur.getColumnIndex("id"));
              adapter.add(task);
          }
          cur.moveToNext();
      }
      cur.close();
      for (int i = tasks.size(); i <= 8; i++) {
          adapter.add(new Task());
      }

      ListView list = (ListView) findViewById(R.id.tasks);

      list.setAdapter(adapter);

      list.setSelection(anchor);
  }

  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Intent setupProcess = new Intent (TaskList.this, SetupWelcome.class);
    boolean first = checkDatabase() ? true : false;

    db = openOrCreateDatabase("priRT.db",
      SQLiteDatabase.CREATE_IF_NECESSARY,null);
    db.setVersion(1);
    db.setLockingEnabled(true);
    db.execSQL("create table if not exists tasks ("
                + "id integer primary key autoincrement,"
                + "name text,"
                + "time integer,"
                + "completed integer,"
                + "timestamp integer,"
                + "spacer integer,"
                + "type text);");
    db.execSQL("create table if not exists schedule ("
                + "id integer primary key autoincrement,"
                + "hours_free integer);");
    if (first) { startActivityForResult(setupProcess,0); }

    populateList();

    Button add = (Button) findViewById(R.id.addTask);
    add.setOnClickListener(onAdd);
    }

    public View.OnClickListener closeTaskListener = new View.OnClickListener(){
        public void onClick(View v){
            int pos = (Integer) (v.getTag());
            Task task = adapter.getItem(pos);
            ContentValues values = new ContentValues();
            if (task.completed == 1){
                values.put("completed", 0);
                task.completed = 0;
            } else {
                values.put("completed", 1);
                task.completed = 1;
            }
            Long time = new Date().getTime();
            values.put("timestamp", time);
            db.update("tasks", values, "id='"+task.id+"'", null);
            populateList();
        }
    };


    private boolean checkDatabase() {
        SQLiteDatabase checkDB = null;
          try {
            checkDB = SQLiteDatabase.openDatabase(
               "/data/data/com.teslaprime.prirt/databases/priRT.db", null,
               SQLiteDatabase.OPEN_READONLY);
            checkDB.close();
          } 开发者_StackOverflowcatch (SQLiteException e) {}
          return checkDB == null ? true : false;
   }

  private View.OnClickListener onAdd = new View.OnClickListener() {
    public void onClick(View view) {
      Intent addTask = new Intent (view.getContext(), TaskEntry.class);
      startActivityForResult(addTask, 2);
    }
  };

  protected void onActivityResult(int req, int res, Intent data) {
    if (req == 0 && res == RESULT_OK) {
        Intent setup = new Intent (TaskList.this, SetupWizard.class);
        startActivityForResult(setup, 1);
    }
    if (req == 2 && res == RESULT_OK) {
        Task task = new Task(data.getStringExtra("name"),data.getStringExtra("type"));
        adapter.add(task);
        ContentValues values = new ContentValues();
        values.put("name", data.getStringExtra("name"));
        values.put("type", data.getStringExtra("type"));
        values.put("completed", 0);
        values.put("spacer", 0);
        db.insert("tasks", null, values);
        Cursor cur = db.query("tasks", null, null, null, null, null, null);
        cur.moveToLast();
        task.id = cur.getInt(cur.getColumnIndex("id"));
        cur.close();
        populateList();
    }
  }

  class TaskAdapter extends ArrayAdapter<Task> {
    TaskAdapter() {super(TaskList.this,R.layout.task,tasks);}
    private List<Task> taskList;
    private Context context;

    public View getView(int pos, View convertView, ViewGroup parent) {
      View task = convertView;
      if (convertView == null) {
        LayoutInflater inflater = getLayoutInflater();
        task = inflater.inflate(R.layout.task,null);
      }
      if (tasks.get(pos).spacer == 0) {
        TextView taskName = (TextView) task.findViewById(R.id.name);
        TextView taskType = (TextView) task.findViewById(R.id.type);
        taskName.setText(tasks.get(pos).name);
        taskType.setText(tasks.get(pos).type);

        Task taskList = adapter.getItem(pos);

        CheckBox closeTask = (CheckBox) task.findViewById(R.id.closeTask);
          if (taskList.completed == 0) {
              closeTask.setChecked(false);
          } else {
              closeTask.setChecked(true);
          }

        closeTask.setTag(pos);
        closeTask.setOnClickListener(closeTaskListener);
        } else {
            CheckBox closeTask = (CheckBox) task.findViewById(R.id.closeTask);
            task.setVisibility(View.GONE);
            task.setFocusable(false);
            task.setClickable(false);
      }

      return task;
    }
  }
}

It may be happening because of the background color of surface in which list appears. Try setting the background color to white in linerlayout and text view coolr black then scroll the through the list view again.