does this mean i have a corruption?

I have a table to which i bulk load datasets of about up to 20,000
 rows at a time. It has a primary key, plus a dataset id (bioassay_id),
however i just ran this query:

bugasbase2=# SELECT bioassay_id, count(*) from mba_data_base where
bioassay_id = 5153 group by bioassay_id;
 bioassay_id | count
-------------+-------
        5153 | 20000
        9712 |   120

bugasbase2=# SELECT bioassay_id, count(*) from mba_data_base where
bioassay_id = 9712 group by bioassay_id;
 bioassay_id | count
-------------+-------
        9712 |  4624


any ideas why bioassay_id 9712 appears in the first query?? does this
suggest corruption somewhere?

thanks for any help

adam

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