...hollow bids....

These bids are generally made for a couple of different reasons, the main one being that traders who feel they have missed the boat use it as a means of creating perceived negatives about the stock. They do this by creating significant optimism when they place the order and then rely on the withdrawal of the order to create some sort of disappointment and pessimism amongst mainly other short term holders.

The other reason is just that it gives a thrill to some silly poor buggers who have an absence of other thrills in their days. Bit sad, but it's a fact.