Access XP Autonumber

I have a table in an Access XP database. The table contains an Autonumber field and a text field, and has 5 records, the autonumber field counts from 1 to 5 as expected, however when adding a new record, the autonumber field does not return 6 as expected, but a higher number every time. I have tried repairing/compacting the database but it does not seem to have any effect. Has anybody had this issue or any idea how to resolve it? I have installed the Office XP service packs (1 and 2)