SAP Note 17069 - ME21 ME31 Referencing: "Function not defined/supported"

Symptom:

If you create a purchase order with reference to a requisition or
contract, or create a contract with reference to a reference document,
and use "Copy + detail" to go from the overview screeen (125/124/122)
to the detail screen, unf from there to the account assignment screen
(item must be assigned), and then press "Continue", the program returns
you to the overview screen with the error message "E: Function not
supported here".

Cause and prerequisites

Program error: Fields OK-CODE and SELFCODE are both still set to KN,
and this function code is not possible on the overview screen.

Solution
See the correction numbers in this Note.
The correction can be implemented in advance as follows:

Program MM06EFAB, FORM ABT_BLAETTERN:

CASE OK-CODE.
.
.
WHEN SPACE.
IF RM06E-EBELP NE 0.
EXIT.
ENDIF.
A-AKTIND = A-AKTIND - A-PAGIND + 1.
WHEN OTHERS. <--- new
IF SELFCODE EQ KNTI. <--- new
CLEAR OK-CODE. <--- new
CLEAR SELFCODE. <--- new
CLEAR DUNKEL. <--- new
A-AKTIND = 0. <--- new
ENDIF. <--- new
ENDCASE.

Program MM06EFBA, FORM BAT_BLAETTERN:

CASE OK-CODE.
.
.
.
WHEN SPACE.
B-AKTIND = B-AKTIND - B-PAGIND.
PERFORM BAT_BLEIBE.
WHEN OTHERS. <--- new
IF SELFCODE EQ KNTI. <--- new
CLEAR OK-CODE. <--- new
CLEAR SELFCODE. <--- new
B-AKTIND = 0. <--- new
ENDIF. <--- new
ENDCASE.

Program MM06EFRF, FORM RFT_BLAETTERN:

CASE OK-CODE.
.
.
.
WHEN SPACE.
IF RM06E-EBELP NE 0.
EXIT.
ENDIF.
R-AKTIND = R-AKTIND - R-PAGIND + 1.
WHEN OTHERS. <--- new
IF SELFCODE EQ KNTI. <--- new
CLEAR OK-CODE. <--- new
CLEAR SELFCODE. <--- new
CLEAR DUNKEL. <--- new
R-AKTIND = 0. <--- new
ENDIF. <--- new
ENDCASE.