I wrote a tiny indior to track spreads on MT4, since I was curious if MT4 traders have these changes in spreads too. Astonishingly, on IBFX the disperse dropped down to zero on many pairs on 02/25/08 in 08:58:02 GMT

I know this happens on ECNs, but was shocked to see it happen in a dealer. I'm still confused as to the reason why. It only lasted of about a second, no actual time to acquire an order in on it, however.