whats going on, page-2

Usually 1 share appears so a broker can perform a "Crossing" (its an on market trade that bypasses the price/time priority). Every broker does it (it is legal and its one of the first things you learn as a SEATS operator).
Basically the two rules are that the market must be 1 price step apart (eg 180.5/181) and the broker must appear at the price they want to cross at. The trade then goes through and the 1 share is removed.

The reasoning behind 1 share being placed at the crossing price is that if it gets knocked out (ie bought or sold) the operator doesn't have to redo the order (they just put the 1 share (or multiples of one share depending how many times they were hit during the day) on the opposite side when finished.

Here endeth the Stockmarket 101 lesson. Go SIP