Description of problem:
Slave mysql in replication could not catch up with master, it doesn't know that master log has been changed already.

Version-Release number of selected component (if applicable):
Version     : 5.0.77
Release     : 4.el5_4.2
both slave and master

OR
slave  4.el5_4.2
master 4.el5_4.1

How reproducible:

Steps to Reproduce:
1. run 'show master status' on master, and notice the 'Position'
2. run 'show slave status' on slave, and notice the 'Exec_Master_Log_Pos'
3. do some update on master, then again run 'show master status', you will notice the position increased.
4  again, run 'show slave status' on slave, and notice the 'Exec_Master_Log_Pos'
  
Actual results:
'Exec_Master_Log_Pos' on slave is still the number you see in the 2nd step. Check the data, still not changed like how master does.

Expected results:
'Exec_Master_Log_Pos' should be the same number to 'Position' in the 3rd step.

Additional info:
slave>show slave status\G
           Slave_IO_Running: Yes
          Slave_SQL_Running: Yes
      Seconds_Behind_Master: 0
master>show processlist\G
*************************** 1. row ***************************
     Id: 3
   User: repl
   Host: 124.238.xxx.yyy:40045
     db: NULL
Command: Binlog Dump
   Time: 2745
  State: Has sent all binlog to slave; waiting for binlog to be updated
   Info: NULL


And, if you type 'stop slave; start slave;' ,the slave CAN catch up with master.

The slave mysql use 4.el5_4.2,and the master mysql use 4.el5_4.1 will result the same. Maybe 4.el5_4.2 replication slave code sucks?