Since 0.4.9, I've been completely unable to access the BitUSD market... I can only guess as to what is happeing, but it sounds like BitUSD is getting heavily shorted. (Edit: with 0.4.9-a I was able to view the markets again.)
I have a possible explanation: It would appear the BTSX market has bottomed, and many traders feel that a strong rebound in price is now imminent. The Chinese have been calling for 0.18 CNY for days, and their target has finally been hit. It's an important technical level, and strong support has been shown. It seems to me that traders with a high level of confidence in a large price increase seem determined to short at almost any price, and people just can't place bids fast enough to keep up with it. We just don't have enough players in the game -- yet.
It's speculation of course, but I wanted to mention this so that people can see there isn't necessarily anything "wrong" with the way the market is operating -- we just need more people to be active in this market. This doesn't happen overnight, especially with the technical issues we've seen. With more participants, I can't see why the peg wouldn't hold.
After the wallet is working better, I am sure all will be well in time. I have every bit of confidence that these bugs in the wallet will be ironed out, so I'm not too concerned about that.