Why do I sometimes have a negative mining profitable?
(Fee higher as Reward)

2014-04-24 23:54:55    0.00001496 BTC   0.00287978    MINING   Block #297513, Reward: 0.00004337, Fee: 0.00002841
2014-04-24 22:51:29   -0.00002027 BTC   0.00286482    MINING   Block #297507, Reward: 0.00004370, Fee: 0.00006397
2014-04-24 20:25:29    0.00002265 BTC   0.00288509    MINING   Block #297494, Reward: 0.00004539, Fee: 0.00002274
2014-04-24 19:33:46   -0.00000975 BTC   0.00286244    MINING   Block #297492, Reward: 0.00004514, Fee: 0.00005489
2014-04-24 17:29:34    0.00002054 BTC   0.00287219    MINING   Block #297490, Reward: 0.00004349, Fee: 0.00002295
2014-04-24 16:36:44    0.00001693 BTC   0.00285165    MINING   Block #297488, Reward: 0.00004352, Fee: 0.00002659
2014-04-24 15:36:40    0.00004391 BTC   0.00283472    MINING   Block #297484, Reward: 0.00004446, Fee: 0.00000055
2014-04-24 15:36:19    0.00003632 BTC   0.00279081    MINING   Block #297483, Reward: 0.00004365, Fee: 0.00000733
2014-04-24 15:19:51    0.00003843 BTC   0.00275449    MINING   Block #297480, Reward: 0.00004364, Fee: 0.00000521
2014-04-24 15:08:40    0.00003570 BTC   0.00271606    MINING   Block #297478, Reward: 0.00004445, Fee: 0.00000875
2014-04-24 14:49:50   -0.00001258 BTC   0.00268036    MINING   Block #297474, Reward: 0.00004424, Fee: 0.00005682
2014-04-24 12:40:51    0.00003463 BTC   0.00269294    MINING   Block #297459, Reward: 0.00004338, Fee: 0.00000875
2014-04-24 12:21:28    0.00003906 BTC   0.00265831    MINING   Block #297454, Reward: 0.00004398, Fee: 0.00000492
2014-04-24 12:09:37    0.00003945 BTC   0.00261925    MINING   Block #297452, Reward: 0.00004383, Fee: 0.00000438
2014-04-24 11:59:46    0.00002999 BTC   0.00257980    MINING   Block #297451, Reward: 0.00004420, Fee: 0.00001421
2014-04-24 11:25:21    0.00003644 BTC   0.00254981    MINING   Block #297449, Reward: 0.00004440, Fee: 0.00000796
2014-04-24 11:09:35   -0.00000874 BTC   0.00251337    MINING   Block #297447, Reward: 0.00004509, Fee: 0.00005383