I get really frustrated with how the market continues after...

I get really frustrated with how the market continues after 4.00pm with many shares traded and of late, the sp dropping.
Could someone please explain how this happens?

Trade of AUT occurring on Wednesday, 02 Mar 2011
52 Week
Time Price Volume Value Condition
04:39:59 PM 3.250 8,820 28,665.00 SX XT
04:13:58 PM 3.148 518 1,630.66 L5 XT
04:10:31 PM 3.160 1,500 4,740.00
04:10:31 PM 3.160 628 1,984.48
04:10:31 PM 3.160 223 704.68
04:10:31 PM 3.160 628 1,984.48
04:10:31 PM 3.160 4,523 14,292.68
04:10:31 PM 3.160 11,620 36,719.20
04:10:31 PM 3.160 5,151 16,277.16
04:10:31 PM 3.160 851 2,689.16
04:10:31 PM 3.160 5,319 16,808.04
04:10:31 PM 3.160 851 2,689.16
04:10:31 PM 3.160 4,257 13,452.12
04:10:31 PM 3.160 3,278 10,358.48
04:10:31 PM 3.160 5,151 16,277.16
04:10:31 PM 3.160 5,151 16,277.16
04:10:31 PM 3.160 851 2,689.16

Cheers in advance.