Looks like bidder u***e was placing bids probably from $435 onwards, but bidder a***b would have had a max bid of $600 placed, thus Auto-outbidding u***e, everytime he placed a bid....(hunting).

When price was upto $600, u***e would have placed a bid of $1050 as his max bid trying to work out what a***b max bid was....
( he wouldn't have placed $1000 as his max, in fear that someone would knock him off with a $1005 bid etc...)

Now the bid is sitting at $1050, and along comes 5***I to place a bid which maxed out u***e's max of $1050, and auto placed a bid at $25 more, being $1075.

Above $1000, bid increments are $25 steps.

Nothing strange there....
MM.