crossed mkts - happens on a regular basis - hard to exploit - quotes are lagging which is usually the cause for u seeing this - check w/ your software provider and check your it connection
it is not quotes that are lagging. it is very simple. Often times the specialist is holding a huge market sell order for example and people are willing to get out 5-10 cents lower then the bid because they KNOW the specialist is about to pull his bid down a lot more. Yes you can consider this an arb, but if the specialist decides to pull his bid down 50 cents, you will be screwed. I have seen it happen a lot of times.