psql version 7.3 can't connect postgres DB version 7.2.3 - using SSH port forwarding

Your name                     : Steffen Schmidt
Your email address      : SSchmid6@urz.uni-heidelberg.de

System Configuration
---------------------
  Architecture                   :  i686 (AMD Athlon)
  Operating System      : Linux 2.4.18.SuSE
  PostgreSQL version  : PostgreSQL-7.3 / PostgreSQL-7.2.3
  Compiler used            : gcc 2.95.3

Please enter a FULL description of your problem:
------------------------------------------------
Just compiled the sources and installed it - seems to work fine ;-) BUT:
I want to access another Postgres database running on version 7.2.3 on another
host, so I normally forward the port 5432(remote) to 5433(local) via ssh.
Typing psql -p 5433 -h localhost mydb works fine for all previous versions of
PostgreSQL but not with 7.3!
I get the error message:
ERROR:  parser: parse error at or near "("

Any clue?
    Thanks
        Steffen

Please describe a way to repeat the problem.   Please try to provide a
concise reproducible example, if at all possible:
----------------------------------------------------------------------
Start PostgreSQL version 7.2.3 on other host
    modify pg_hba.conf for local access with full IP-Address
    start postmaster with option -i
Forward port 5432 from remote host to local host via ssh
    ssh  -L  5433:remote_host:5433 remote_host
Try to access remote DB with psql (Version 7.3):
    psql -p 5433 -h localhost -l

=> ERROR:  parser: parse error at or near "("