If you're watching Level2 and just saw available shares at .0047 jump up by 10m (and immediately back down) that was me demonstrating this. I put in a sell order at .0047 for 10m shares, then cancelled it. The ASK responded accordingly. That's where these crazy walls come from.
My vote: If you want to sell, wait for the price to get where you want it before placing your order. Otherwise you're blocking your own progress.