update returns 1, but no changes have been made

I have been trying to update a table -- the update statement returns 1
indicating that one row has been updated, but no changes were made. 

This is happening on two servers: 
      1.my development server, running Postgres 7.0.3, RedHat 7.1       2.soon-to-be production server running Postgres
7.1.3,RedHat 6.2 
 

Could I have a deadlock? Something else?  

What should I be looking for?

Thanks.
JT
________________________________________
James Thornton, http://jamesthornton.com