automatic login, how?

I'm trying an automatic login. Currently, I try

  tn5250 \
     trace=5250.log \
     map=273 \
     env.DEVNAME=SCHURIGH \
     env.IBMRSEED= \
     env.USER=USER \
     env.IBMSUBSPW=USERPW \
     as400

According to rcf2877, the transfer should look like this:

  AS/400 Telnet server             Enhanced Telnet client
  --------------------------       -------------------------
  IAC DO NEW-ENVIRON          -->
                              <--  IAC WILL NEW-ENVIRON
  IAC SB NEW-ENVIRON SEND
  USERVAR "IBMRSEEDxxxxxxxx"
  USERVAR "IBMSUBSPW"
  VAR USERVAR IAC SE          -->
                                   IAC SB NEW-ENVIRON IS
                                   VAR "USER" VALUE "DUMMYUSR"
                                   USERVAR "IBMRSEED" VALUE
                                   USERVAR "IBMSUBSPW" VALUE "yyyyyyyy"
                              <--  IAC SE

Howvever, according to 5250.log, the transfer is

  GotSB:<IAC><SB><NEWENV><SEND>
          <USERVAR>IBMRSEED<05 D6 15 34 BD A8 24 5E>
         <VAR><USERVAR><IAC><SE>
  SentSB:<IAC><SB><NEWENV><IS>
          <VAR>DEVNAME
          <USERVAR>SCHURIGH
          <VAR>IBMRSEED
          <USERVAR>
          <VAR>USER
          <USERVAR>SCHURIG
          <VAR>IBMSUBSPW
          <USERVAR>SCHURIG
          <VAR>TERM
          <USERVAR>IBM-3179-2<IAC><SE>

Now I'm mildly confused. The RFC shows me two different sequences of 
either "VAR xxx VALUE yyy" or "USERVAR xxx VALUE yyy". But the 5250.log 
tells me it sends sequences of "VAR xxx USERVAR yyy" and no VALUE 
altogether.

Who is wrong?