Detailed description here: http://www.zabbix.com/forum/showthread.php?p=121861#post121861

Text:

I'm testing stock Zabbix 2.0 before upgrading my production server, and while testing low level discovery, which is a fantastic new feature, I found out that when I change a graph on Graph Prototypes, it does not reflect on existing graphs already populated on low-level discovered items.

My test scenario is:
Stock Zabbix 2.0 installation with example data
Two 3Com Switches on a stack
A new host created pointing to SNMP interface of switch, and templated linked to Template SNMP Device

After doing this basic configuration, Zabbix found out all 120 interfaces, including Vlan and link aggregation Interfaces (awesome!), and started to collect all items configured on Template SNMP Interfaces, letting me check the graphs of traffic on those interfaces. But no change is reflected on those graphs when I edit Template SNMP Interfaces.

Is this the normal way of operation, or I'm doing something wrong?

Edit: just for information: I tried to change the Draw Style of one of Items from Gradient Line to Bold Line.