[web2py] Exception not thrown for duplicate values.

[rahulserver]

I am importing data from a csv file and the field declaration is 
as:Field('Account',requires=IS_NOT_EMPTY(),unique=True). But no exception 
is thrown when duplicate values for the field is imported!  In one of the 
posts, I have read that it is an sqllite specific issue which I am using 
for backend How to get round it?