[noxn]

I accept that your explanation makes sense, but the fact that this can happen automagically in an intransparent way when someone just wants to buy a number of shares at a quoted price just feels wrong. And reading a few other articles on Nanex also give me weird image of what happens in stocks in general.

Then again, I have no idea about these things and should probably shut up.

[throwaway283719]

Just remember that when you say

  "someone wants to buy a number of shares at a quoted price"

what you really mean is

  "a giant investment bank or hedge fund with some privileged
   information about a stock wants to buy so many shares that
   they actually need to go to multiple exchanges to satisfy 
   their demand"

and you'll be all set ;)