validates_uniqueness_of fails on update

According to the docs when you validate on uniqueness it is supposed
to skip the check on the column. I am getting failed validation on
updates for some reason. Rails 2.3.5

Please provide more information about (or just check) your migration
and model and its associations.

In the meantime, ActiveRecord skips the check on the record/row (not
the column) on Update. Here's the relevant text:
"When the record is created, a check is performed to make sure that no
record exists in the database with the given value for the specified
attribute (that maps to a column). When the record is updated, the
same check is made but disregarding the record itself. "

Have you verified your data, that there is only one record in the
table with that value?