Reproducing FragmentStatePager bug: https://code.google.com/p/android/issues/detail?id=19001&can=1&q=FragmentStatePagerAdapter&colspec=ID%20Status%20Priority%20Owner%20Summary%20Stars%20Reporter%20Opened

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin">

    <android.support.v4.view.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:background="@android:color/holo_blue_dark" />

    <Button
        android:id="@+id/remove_0_btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="remove0" />
</LinearLayout>

MainActivity.java

package com.nakama.checkfragmentstatebug;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    public static final String TAG = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager());
        ((ViewPager) findViewById(R.id.view_pager)).setAdapter(adapter);
        findViewById(R.id.remove_0_btn).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                adapter.remove0();
            }
        });
    }

    private static class MyPagerAdapter extends FragmentStatePagerAdapter {

        private List<String> data = new ArrayList<>(Arrays.asList(new String[]{"0", "1", "2"}));
        private List<Fragment> fragments = new ArrayList<>(3);
        private boolean removed = false;

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public int getItemPosition(Object object) {
            int index = fragments.indexOf(object);
            int ret = index != -1 ? index : POSITION_NONE;
            Log.d(TAG, "getItemPosition object:" + object + ",ret:" + ret);
            return ret;
        }

        @Override
        public Fragment getItem(int position) {
            Fragment f = MyFragment.newInstance(data.get(position));
            Log.d(TAG, "getItem:" + position + ",f:" + f);
            while (fragments.size() <= position) {
                fragments.add(null);
            }
            fragments.set(position, f);
            return f;
        }

        public void remove0() {
            if (!removed) {
                removed = true;
                data.remove(0);
                fragments.remove(0);
                notifyDataSetChanged();
            }
        }

        @Override
        public int getCount() {
            return data.size();
        }
    }


    public static class MyFragment extends Fragment {

        public static MyFragment newInstance(String data) {
            Bundle bundle = new Bundle();
            bundle.putString("data", data);
            MyFragment f = new MyFragment();
            f.setArguments(bundle);
            return f;
        }

        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            TextView textView = new TextView(getContext());
            textView.setText(getArguments().getString("data"));
            textView.setTextSize(24);
            textView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
            textView.setGravity(Gravity.CENTER);
            return textView;
        }
    }
}

Reproducing process:

1. Open app.
2. Check a page with text '0' is displayed.
3. Tap remove0 button to remove a page 0, and check now a page '1' is displayed.
4. Swipe left, there should be a page with text '2', but practically there is an empty page. Is it bug?