When is %EOF not an %EOF

To the list,
I seem to run into this problem every once in a while:

Using a partial key to perform a CHAIN and READE loop the chain does not
find any records but still goes into the loop.  The code looks something
like this -

Partial_key   CHAIN    FileName                    88
                      DOW       NOT %EOF     vs.     *IN88 = *OFF
                      ...
                      ...
Partial_key   READE  FileName                             88
                      ENDDO

If I replace the %EOF with an indicator  (DOW    *IN88 = *OFF and the READE
with the 88 in the "=" indicator position), it works like I expect.  My
customer's box is at V4R5.  Could I be imagining this or what?

TIA...
Eric