Size of Binary log file in Mysql Replication

I have a master - server replication setup in Linux servers.

Master Configuration details :

 MySQL version is 5.1 and replication mode is MIXED type.

Slave Configuration details :

 MySQL version is 5.6

If i insert single record , then it is getting replicated to slave.

When i am running a script to insert thousand of records at master , it is not getting replicated.

When i see the size of binary log file , it is of 908 MB and when i see the size of relay log file , it is 560 KB.

Does , size of a binary log file matters ?
or what is the probable cause of this.

Below is master cnf details :

  [mysqld]

  datadir=/var/lib/mysql
  socket=/var/lib/mysql/mysql.sock
  user=mysql
  # Disabling symbolic-links is recommended to prevent assorted security risks
    symbolic-links=0
    bind-address = #master IP# ( not showing here )
    port=3306
    wait_timeout=90
    net_read_timeout=90
    connect_timeout=90
    max_connections=100
    lower_case_table_names=1
    log-bin=mysql-bin
    binlog_format=MIXED
    server-id=1

[mysqld_safe]
     log-error=/var/log/mysqld.log
     pid-file=/var/run/mysqld/mysqld.pid