There is some bug in the order book chart:
http://bitcoinity.org/markets/btce/USDIf I click the minus sign, the vertical scale goes from 0-100 to 0-15, when it should go to a larger scale. See images, before:
....
+ = Zoom In
- = Zoom Out
Seems to work ok for me.
It works OK now, but on the posted images it is obviously wrong.
The bottom image apparently has the y scale set to the "buy" (green) line (you can compare it to the upper image, the extreme point is in both on about 129,35 BTC (x-axis) and 15 (y-axis)), while "sell" (red) has much bigger values the the y-scale of 15 and is out of graph range (for example at the price of 131.0 BTC you can see in the upper image that the size is about 60-75).
In short: the code to determine the y range took the "green" value instead of the larger "red" value.