Fields updated that shouldn't be

I've got a program bug that I cannot figure out and would appreciate some
help. This is written in RPG using SQL on V5R2. Let's assume for sake of
simplicity that I'm using data for one calendar year - 2008.

Program1 reads records from FILE1 delivered by SQL and writes to FLDA in
FILE2. Since it's calculating a 60 period average it can't begin until it
has 60 records. So we don't see any records written to FILE2 until
03/28/08.

Program2 reads records from FILE1 delivered by SQL and writes to FLDB. It's
performing a different calculation that requires 15 days of data. So we see
it begin writing recors on 01/15/08.

Here's where the problem starts. I was looking over the data and noticed
that FLDA had data in it for the records from 01/15/08 to 03/27/08. It is
filled with the exact number in FLDA from 12/31/08. So I think the problem
must be something in Program2 but can't find anything. Even though it is
updating the same records I can't find any way it would update FLDA.

Then I decided to try an experiment. I reset my test data, ran Program1
again and then ran Program3 (they aren't necessarily sequential), which
reads records from FILE1 delivered by SQL and writes to FLDC in FILE2.
Guess what? It does exactly the same thing - updates FLDA!!

My only guess at this point is that I've got something wrong in the way I
update FILE2. Here's how I do it:

1. Build key with KLIST
2. CHAIN to FILE2
3. If indicator is off, UPDATE
4. If indicator is on, WRITE

Any suggestions would be greatly appreciated. TIA.


Jim Newman