This concerns me most when I see a head and shoulders top. As soon as its almost certain that the stock will drop, the prices cross. You will never convince me that its a stale quote. It happens too often on head and shoulders to be a coincidence.
In this case I see these are all (except Q's) NYSE symbols. So my initial explanation about the symbol being traded on different ECN's is not valid.
I see them from time to time also. Usually during pre-market or after-market. And also during heavily traded volume stocks, such as Google. Although, I Never tried to buy from one of them.
in 2000 I made 1200 % on my acct taking advantage of stuff like this. sigh ... memories ... should have taken my profits and bought some land somewhere !
In my experience if you see it during RTH you should probably ignore it. However during AH it is not uncommon for different ECN bid/asks to be crossed and IF you are very careful you can profit from the disparity. I've done it successfully on a number of occasions.
Somebody was flashing an ask lower than the bid AH awhile back. It was something like .30 or .40 lower than the bid. It was extremely annoying at the time so I put in a buy order at that price. Anyway, I got hit and sold it a second or so later for a nice profit.
Also, for listed stocks anyway, BRUT will show a short-sale order at the limit price that the user entered, even if it will not execute at that price, sometimes even if it crosses other ECNs. For example: ABC NBBO is 50.00 - 50.15, last CQS print is an uptick at 50.13. If you enter a short-sale on BRUT at 50.11, it will display an offer of 50.11, even though it won't execute unless someone sends BRUT a buy order at 50.13 or higher, or a print goes off at 50.10 or below (to make 50.11 a legal short-sale). During extended hours, it's even worse. If you enter a short-sale order at 49.00, BRUT will display an offer at 49.00, crossing the bid by 1.00, and yet won't execute at anything less than a legal zero-plus tick. I don't know if this happens during RTH, too (that it will cross other markets if they were there first). Sure would be nice if Naz would fix this, now that they own it. Or better yet, get rid of BRUT.