If the bidding increment is $0.50 then the next bid must be at least $0.50 higher than the current high bid.

Since your max bid was $25.00 then I assume that you were the current high bidder at a bid less than $25.00. Let's say that you had the current high bid of $15.00 with a max high bid of $25.00. If someone bids $16.23 then EBay will automatically place a bid of $16.73 for you. $16.73 becomes the current high bid. However, if someone places a bid of $25.01 (which happened in your case), then that becomes the high bid which is at least $0.50 higher than the last current high bid of $16.73 and higher than your max bid or $25.00. If the winning bidder had placed a bid of $25.75, then the winning bid would have been $25.50.

If your max bid had been $25.02 then you should have won the auction for $25.02.

Hope that this explanation is not too confusing.