BUG #13979: Strange pg_stat_statements results with PREPARE/EXECUTE

The following bug has been logged on the website:

Bug reference: 13979
Logged by: Kasahara Tatsuhito
Email address: kasahara(dot)tatsuhito(at)gmail(dot)com
PostgreSQL version: 9.5.1
Operating system: RHEL
Description:

Hi, I noticed that in some cases pg_stat_statements shows strange results.
(example)

=# CREATE TABLE tt(c1 int);
=# INSERT INTO tt SELECT generate_series(1,10);
=# SELECT pg_stat_statements_reset();

Then, performed simple SELECTs via java. (see the end of this mail)
After that, I got the following pg_stat_statements result, and ISTM it's
reasonable.

=# SELECT queryid, calls, query FROM pg_stat_statements WHERE query LIKE
'%tt%';
queryid | calls | query
-----------+-------+--------------------------------
575935600 | 10 | SELECT * FROM tt WHERE c1 = $1

Next, reset the pg_stat_statements and performed PREPARE and EXECUTE via
psql.

=# SELECT pg_stat_statements_reset();
=# PREPARE p1(int) AS SELECT * FROM tt WHERE c1 = $1;
=# EXECUTE p1(1);
=# SELECT queryid, calls, query FROM pg_stat_statements WHERE query LIKE
'%tt%';
queryid | calls | query
-----------+-------+----------------------------------------------------
575935600 | 1 | PREPARE p1(int) AS SELECT * FROM tt WHERE c1 = $1;
(1 row)

Then, performed same SELECTs via java.
After that, I got a bit strange pg_stat_statements result..

=# SELECT queryid, calls, query FROM pg_stat_statements WHERE query LIKE
'%tt%';
queryid | calls | query
-----------+-------+----------------------------------------------------
575935600 | 11 | PREPARE p1(int) AS SELECT * FROM tt WHERE c1 = $1;
(1 row)

I'm not sure it's expected behaviors, but seems a bug.

Best regards,

// Java Test code
import java.lang.*;
import java.sql.*;

class Test {
public static void main(String[] args) {
String driver = "org.postgresql.Driver";
String url =
"jdbc:postgresql://localhost/postgres?user=postgres&ApplicationName=my_jdbc_test";
try{
Connection con = DriverManager.getConnection(url);
con.setAutoCommit(false);
String sql1 = "SELECT * FROM tt WHERE c1 = ?";
PreparedStatement ps1 = con.prepareStatement(sql1);

for (int i=1; i<=10; i++) {
ps1.setInt(1,i);
ResultSet rs = ps1.executeQuery();
while(rs.next()){
System.out.println("results c1:" + rs.getInt(1));
}
}

con.commit();
ps1.close();
con.close();
}catch (Exception e){
e.printStackTrace();
}
}
}