Problem with iconv: what could I be doing wrong?

I have a function that calls iconv, in one module, called by a main program in another module. It works the first time, but it fails on subsequent calls.

In the called module, I have global static buffers defined thusly (white space squeezed out to avoid line breaks):

D DS
D BUFFY 1 500000A
D BUFFA 1 500000A DIM(500000)
D BUFLEN S 10I 0
D MUFFY S 500000A
D MUFLEN S 10I 0 INZ(500000)

and I have parameters for iconv defined thusly:

D QtqCode_T Ds
D Qtq_CcsId 10i 0
D Qtq_CnvAlt 10i 0 Inz( 0 )
D Qtq_ShfSttAlt 10i 0 Inz( 0 )
D Qtq_InpLenOpt 10i 0 Inz( 0 )
D Qtq_ErrOptMxd 10i 0 Inz( 0 )
D Qtq_Rsv 8a Inz( *Allx'00' )
**
D fromcode s Like( QtqCode_T )
D tocode s Like( QtqCode_T )
**
. . .
D pBUFFY s * Inz(%Addr(BUFFY))
D pMUFFY s * Inz(%Addr(MUFFY))

At the top of the procedure, I'm clearing BUFFY, BUFLEN, and MUFFY, and reinitializing MUFLEN to 500000, the length of MUFFY. Then, once I have a UTF-8 value in BUFFY, I have:

C Eval Qtq_CcsId = 1208
C Eval fromcode = QtqCode_T
C Eval Qtq_CcsId = 37
C Eval tocode = QtqCode_T
**
C Eval iconv_t = IconvOpen( %Addr( tocode )
C : %Addr( fromcode )
C )
**
C EVAL RC = ICONV(ICONV_T:
C pBUFFY:
C BUFLEN:
C pMUFFY:
C MUFLEN)
C EVAL RC = ICONV_CLOSE(ICONV_T)
C EVAL BUFFY = MUFFY
C EVAL BUFLEN = %LEN(%TRIM(BUFFY))

I then go on to parse the translated buffer

The main program calls this procedure three times. The first time, it works fine. The second time, it comes back with MUFFY completely blank.

I just tried adding statements to reinitialize pBUFFY and pMUFFY at the top of the procedure; no change.

I have no idea what I could be doing wrong here.

--
JHHL