This sometimes happens when a Proxy Bid is active.

In some cases, it's possible that another bidder's standing maximum (Proxy) bid is greater than yours, but by less than the bid increment. In this case, the other bidder will be winning at exactly their maximum bid.

For example, consider an auction with an opening bid of $10 and a bid increment of $2.00.

The current winning bid shows as $18.00, but that bidder indicated a maximum bid amount, or Proxy Bid, up to $25.01. This maximum bid amount is not disclosed until another bidder places a bid that is more.

If you now place a bid for $25.00, your bid will be superseded by the other bidder's Proxy of $25.01. The other bidder will have won by only one penny even though the minimum bid increment is $2.00. The reason for this is that the minimum bid increment is measured at the time the bid is originally placed. At the time the other bidder placed the Proxy Bid of $25.01, the current auction bid for the item was less than $18.00, so the bid increment was more than the minimum $2.00.