This graph is showing 2 days worth of data.
http://i.imgur.com/FTF1S.png

I started polling for data nearly 6 days ago, so I have 5 days+ worth of data to show. I can show 1 days worth of data going back 5 days.

When I expand the graph to include the last 3 days, it then says "no data" and the graph is blank.
http://i.imgur.com/e8rDD.png

However if I simply make my browser bigger and hit F5, it reappears due to larger image...
http://i.imgur.com/YR9bj.png

Here is the graph configure page,
http://i.imgur.com/bO9NS.png

Data is an iptables parser giving an integer stored as delta (speed per second)

Zabbix 1.8.10 on Debian wheezy/sid, compiled from source with,
./configure --enable-server --with-mysql --with-jabber --with-libcurl --with-net-snmp --with-ssh2