Unsure this happens only on our Zabbix 1.6.6 deployment
(Sorry but haven't tested in Zabbix 1.7)

If a Pie or Exploded Graph being fedback with a unique Item always has the same shape regardless of the actual item's value (46%, 73%, 90%, whatever, always shows a full pie chart)

The graphs shape should adapt to current value allowing to easily recognize the monitored Item health(they're useful for % metrics).
Pie and Exploded layout should be polished to a more professional look