Addled index

We've faced with strange index problem.

At some moment index became bad and queries does not return any data.

For example, there are two tables - A (id, name) and B (id, name, a_id).
B.a_id is foreign key to A. Both name columns in tables contains identical
values for A.id = B.a_id. A.name column has unique constraint and
additional index by it.

So, in some moment results for queries like [select id from A where name =
'petya'] became empty (row with 'petya' name exist in A).

But query [select a_id from B where name = 'petya'] returns A.id and
[select * from A where id = <found id>] returns row.

This problem can be solved by index recreation only.

How can we avoid such situation?

--
Oleg V Alexeev
E:oalexeev(at)gmail(dot)com