Redstone Comparator ERROR

Redstone Comparator can't output enough energy.

Theoretically>> If there're "64,64,64,55" item in the box, the comparator should output 2 block of energy.

[ http://i.imgur.com/EWEpRv0.png ]

If it use the other way for put the items in. >> First,the box have 64,64,64,54 stones. When I put the last one item in the hopper and connect it with the box.

[ http://i.imgur.com/n4cTm1k.png ]

Finally,it can't output enough energy in spite of there're "64,64,64,55" item in the box . unless you open the box or change the comparator to upload block.

[ http://i.imgur.com/bIrQMnZ.png ]
[ http://i.imgur.com/KksqlL8.png ]

Using Hopper put the items in cannot work!!!!!!

This is GIF proof:
[ http://i.imgur.com/SR1cO0p.gif ]