whats the difference on this update.

A coworker has come to me on this and I don't have the answer.  Here is
the situation
 
a copy of a production physical was created in test library via CPYF.
Logical was built over the copied file. 
Program does a read loop on the file updating records in the test
library.  The program updates as desired. 
 
Same program over the production file when it updates a record, proceeds
to read the same record again.  
The field that is being updated is not  one of the key fields. 
 
I have verified the logical in test and the logical in production are
the same.  
 
The only real difference i can find in the physical file is that the
production file is journaled. Could this be the cause?
There is only 1 copy of the program.  
 
Any idea what may cause this situation?  
 
 
Thanks 
 
Mike