Currently, a person can lower his bid below the amount of the second highest bid (+1), effectively revoking his bid. It should only be possible to lower your bid below what has already manifested. For example:
Alice bids 10 on X, Bob bids 5 on Y. Alice's bid manifests to 6. She may lower her bid to 6 at this point, as it doesn't effectively lower the visible bid, but she must not be able to lower her bid any lower.
Currently, a person can lower his bid below the amount of the second highest bid (+1), effectively revoking his bid. It should only be possible to lower your bid below what has already manifested. For example:
Alice bids 10 on X, Bob bids 5 on Y. Alice's bid manifests to 6. She may lower her bid to 6 at this point, as it doesn't effectively lower the visible bid, but she must not be able to lower her bid any lower.