Function key indicators

I am attempting to 'genericize' the routine I use to test for the 'dup' key
use.
 
I would like it to be generic enough so that it would work without
modification when the length or layout of the input data changes.
Most screens have I, O,and B data interspersed.
(## represents the 'screen number id')

To do this I declare the input buffer (Input## - LikeRec(PgmScrn##:*Input)).
I cycle through the input data structure character by character substituting
any found 'dup' characters with the corresponding character from a 'saved'
input buffer (PrvInput03  S   1 Dim(%Len(Input##))), until I get to the end
(%Len(Input01)). For this to work I changed my typical (all I ever use)
'exfmt' with a 'write format' line, followed by a 'read-formatname-data
structure' line.
(I could not figure out how to automatically fill the input buffer data
structure using 'exfmt')

This works fine. However, changing from 'exfmt' to 'read-formatname-data
structure' stops the function key indicators (*InKA-*InKY) from
automatically being set on when the corresponding function key is pressed.

If I remove the data structure name from the 'read' line, hitting a function
key DOES set on the corresponding *InK? indicator automatically, just like
when I used 'exfmt'.
Why does the absence/presence of this data structure name change this?

Is there a way to set up the screen 'reads' so that functions keys
automatically set on the corresponding *InK? indicator (like 'exfmt' does)
AND the input buffer data structure gets filled automatically like when the
'read-formatname-data structure' method is used?

(Because of legacy issues I cannot (do not want to) use *In01-*In99 to
represent the function keys without a lot more code modifications than I
care to do.)
Or is there a different way of declaring the input buffer so that all input
fields are contiguous and its length can be determined?

Thanks in advance for any help.

Tim Kredlo
Exterior Wood, Inc