Problem:

FD  VAR-LENGTH-REC-FILE               

     LABEL RECORDS ARE STANDARD.       

01  REC1 PIC X(10).                   

01  REC2 PIC X(20).                   

01  REC3 PIC X(30).                   

but when it gets written all records are 30 bytes long.

Resolution:

Adding RECORDING MODE V corrected the problem.