I see that this happen time to time. I think it is simply delay on websocket interface. I have no idea how many connection that websocket interface has, but I believe it can be in thousands.
I don't know whether your explanation for the fault is accurate. At least it didn't seem to me that it was a delay. I saw a half hour of the price being up to $3 more than the feed and then within minutes being $3 less (of a different price) - this six dollar swing was happening while the price was spiking on the feed (as shown in the image above).
This is a pretty serious issue no matter what is causing it. And right now MtGox is down again. This really doesn't make one confident of trading there
