Bidding in multiple drop auctions and pre-release auctions across many platforms, it is common and smart for people to place their bids at the last second, especially in snapnames and namejet pre-release auctions since when there is a bid on the domain it is seen publicly and this draws attention to the name. There have been many domains especially at namejet which go from 0 bidders to several bidders within the last seconds, this part of last minute bidding / backordering is common.
The other part, unusual bidding is something I've also encountered, though it is a difficult thing to pinpoint. Since the other person bidding is not something public there is a lot of room for abuse on the auction-end and just as much room for speculation/conspiracy on the other end. I think there should be much more transparency with auction-houses everywhere. If a bidder bids someone up but rarely/never wins then this is where a potential problem exists. This is a hard thing to identify without statistics of bidders and win/loss ratios. It is best NEVER to place a large proxy bid ahead of time. Even if nothing "funny" or tempting occurs on the auction-house's side, there is still the potential for the auction to go higher earlier on, leading to even higher bids at auctions-end. One auction I remember was one in which I never expected other bids/interest in. It was very low search, had little or no traffic, and was something that had more personal meaning than something that was popular and well known to others. Placing a high proxy bid, the domain went up several hundred percent to within just dollars at the very end of the auction. The bidder was not a name that was recognized and it just seemed "odd" how it went from xx to high xxx within dollars all from the same previously unknown bidder who never seem to win. There is plenty of room to speculate about auction-side fraud given the ambiguity from lack of publicly available data, not to mention it has happened before. With more disclosure, a lot of this could be put to rest and create a more open and fair bidding environment.