index with no column

With this group's help (which is MUCH appreciated, thanks) I am slowly
starting to live with Postgres in a production environment.

I have setup an automated backup/restore between two machines, all is
fine. Bar on thing: after restoring mu database, I had a message about
several errors ignored (I did not keep a log of these errors), but I
am seing on several tables, some indexes declared but pgadmin3 fails
to show any columns. I had to manually drop the indexes and recreate
them

So my questions are

- How is this possible ? Should'nt the index be rejected during the
restore if there was a problem ?

- Is there a query I could write to check what are the indexes w/o
columns defined ?

Thanks in advance

Didier