deadlock detected

I recently tried to deploy Postgresql in a highly active environment.
My use of data was probably a little unusual, in that I was constantly
modifying several fields within a table, one of them being a text
string.  Literally hundreds of thousands of these kinds of changes would
be made every day.  One problem that I can report for certain is
receiving 'deadlock detected' messages.  Thing is, I was never doing
transactions, just pg_exec/pg_select commands from libpgtcl.  No
transaction (ie. BEGIN .... COMMIT) commands were issued.  Why would I
ever get a deadock?

The environment was a server on a Tru64 5.1 running on a dual CPU Alpha
server.  PostgreSQL version 7.2.1.  Sorry I can't give you more detail.
I had put it in a production environment not expecting a problem like
this, so I've had to roll back my changes.

Regards,
Randy Kunkee