SFLMSGKEY on Message subfile

Im having problems with my message subfile, this is the DDS:

A          R SFLMSG                    SFL
A                                      SFLMSGRCD(23)
A            @SFLMSGKEY                SFLMSGKEY
A            @SFLPGMQ                  SFLPGMQ

A          R SFLMSGC                   SFLCTL(SFLMSG)
A                                      SFLSIZ(0002)
A                                      SFLPAG(0002)
A                                      SFLDSP
A  57                                  SFLINZ
A N57                                  SFLCLR
A  58                                  SFLEND
A            @SFLPGMQ                  SFLPGMQ

Im setting @SFLMSGKEY with the ID of the first message that i want to show
in the subfile, *in57 = *on (SFLINZ) and then write the subfile control.
This doesn't seem to work, 'cos im seeing in the subfile some previuos
messages not related with the ones I just sent.
Note that this is a page-at-a-time subfile (SFLSIZ=SFLPAG), one solution
that i've found is to delete my previuos messages from the program queue
with the Receive Message API, but this doesn't work completly becouse i
can't be completely aware of the previuos messages, such as "record locked"
and other internal messages of the running program.

Making SFLSIZ greater that SFLPAG wouldn't fit this scenario, so please,
restraint making that suggestion.

Thanks in advance,

Carlos K.