I was just browsing the AH, and found a few auctions for valuable items with a bid of zero. Biding on them doesn't work obviously. I wonder if they are placed to catch AH bots or something like that...
Here's a screenshot:
or is there a simpler explanation? Can you post an item with 0 starting bid and thus break the system?
From my experience, this is a bug. I don't think it's an Expired auction or a Cancelled auction like others have mentioned.
The reason I say this is because I bid on an item earlier today. It was showing on my Auctions tab and I later got outbid. I tried to bid on it from my Auctions tab but was unable to, even though there were a few hours left to the auction (I knew there were a few hours left on the clock because I bid on it earlier and also it showed the proper time left in the AH). I tried to search for the item and once I found it, it showed with 0 bid in the Search tab.