As soon as a low ask gets depleted it gets replenished, the bids are not touched:
Orders Lots Bid Ask Lots Orders
2009Apr3 12:00 ET
10 95 0.530 0.540 3 1
12 121 0.520 0.550 122 9
11 246 0.510 0.560 218 9
8 481 0.500 0.570 57 6
2 24 0.495 0.580 91 7
2009Apr3 12:01 ET
10 95 0.530 0.540 20 1
12 121 0.520 0.550 122 9
11 246 0.510 0.560 218 9
8 481 0.500 0.570 57 6
2 24 0.495 0.580 91 7