NOTICE from vacuum - Mailing list pgsql-general

I am getting the following NOTICE from vacuum:

NOTICE:  Index tag_surveys_d_field_survey__key: NUMBER OF INDEX' TUPLES (6475) IS NOT THE SAME AS HEAP' (6474)

How does such a thing come about?  Do I just drop the index and remake
it?  Is the index or the heap correct?

Thanks for your help.

Cheers,
Brook