The key fields are block value, your shares and the total.
3819937 794 0.00124563 25.45165437
32470080 15383 0.00859605 25.26860000
4629094 2388 0.01508919 25.29600000
5689208 2550 0.01025923 25.21487399
23468644 7472 0.00788146 25.25990000
Now the basic formula is (Block Value * 0.98 * your shares) total shares. The .98 is because Slush takes 2% for his costs time managerial fee
So you're theoretical earnings are for each block
0.005184494 -0.0039388642
0.011731808 -0.0031357578
0.012788401 +0.0023007888
0.011075702 -0.0008164716
0.007881458 ~0
Total = 0.0486618628
Leaving you -0.0055903028
This could be a fault. I expect however its down to the true formula being a little more complex. Older shares are worth less to discourage attempts to cheat the system. Its probably just coincidence with the crash and you're mining rates were fastest at the start of blocks.
Im sure you've noticed the hash rate fluctuates a little bit. Not to mention, if you started stopped the miners at all then bad timing could leave you with earlier less worthy shares.
If you are still concerned let me know, i'm about to get out of newbie mode so can put a copy of this in the slush's pool thread.