validates_uniqueness_of in 2.1

I updated an application from Activerecord 2.0.2.9216 to 2.1.0 and now validates_uniqueness_of doesn't seem to be working. The unique constraint was caught by the activerecord validation in 2.0.2, but now it's getting past that and being caught by the database instead.

When I do a gem 'activerecord' '=2.0.2.9216' before activerecord require it works again.