Very new to this concept, why would something like this occur on Bitminter's pool?

Completed Duration Difficulty Pay/Hour at 1 TH/s Total Thps Your Ghps Your work 2014-10-25 15:02 1h 46m 35,985,640,265 being paid now 2,436.1 10.7 15,856 2014-10-25 13:15 2h 15m 35,985,640,265 being paid now 1,896.0 10.9 20,718 2014-10-25 10:59 2h 13m 35,985,640,265 being paid now 1,935.6 10.4 19,340 2014-10-25 08:45 2h 26m 35,985,640,265 being paid now 1,767.4 10.2 20,756 2014-10-25 06:18 2h 30m 35,985,640,265 being paid now 1,721.0 10.3 21,688 2014-10-25 03:48 2h 11m 35,985,640,265 being paid now 1,951.9 10.2 18,872 2014-10-25 01:36 2h 36m 35,985,640,265 being paid now 1,646.6 10.4 22,722 2014-10-24 22:59 2h 35m 35,985,640,265 being paid now 1,653.5 10.2 22,314 2014-10-24 20:23 2h 37m 35,985,640,265 being paid now 1,641.0 10.9 24,036 2014-10-24 17:46 2h 36m 35,985,640,265 being paid now 1,649.8 10.8 23,620 2014-10-24 15:09 2h 35m 35,985,640,265 ? 1,664.1 10.6 22,992 2014-10-24 12:34 2h 37m 35,985,640,265 0.00000000 1,642.0 10.0 21,882 2014-10-24 09:56 2h 36m 35,985,640,265 0.00000000 1,650.2 10.3 22,502 2014-10-24 07:20 2h 29m 35,985,640,265 0.00000000 1,724.3 10.4 21,844 2014-10-24 04:50 2h 09m 35,985,640,265 0.00000000 1,996.7 8.5 15,322 2014-10-24 02:40 2h 34m 35,985,640,265 0.00057673 1,673.0 0.2 432 2014-10-24 00:06 2h 26m 35,985,640,265 0.00057673 1,756.1 0.2 354 2014-10-23 21:38 1h 41m 35,985,640,265 0.00057673 2,544.7 0.2 222 2014-10-23 19:57 1h 34m 35,985,640,265 0.00057673 2,736.5 0.2 212 2014-10-23 18:22 2h 00m 35,985,640,265 0.00057673 2,135.9 0.2 284

In some cases, next to no work was done - and small reward was found. In others, far more was contributed, but the pay is zero.

I ask on the heels of switching from cgminer to bfgminer; could this be the cause? Is the timing otherwise purely circumstantial?

Thanks!