SQLITE unique index : select is not working on the columns with unique indexes

the problem occurred at run-time when one of the systems just stopped working because of a select query failing on a table where there was a unique index on a column. there are 5 columns and one has a unique index on it such that.

table abc with columns c1, c2, c3, c4, c5

c2 has a unique index on it when we do

select * from abc where c1 = 1;

it works fine and works fine for all other columns but when we do

select * from abc where c2 = 1;

it does not return any thing.

later i discovered the same problem with all the tables which had unique indexes

the only guess I have is that the indexes have been screwed up for some reason but why and how and how to prevent it happening in future?

Please help.