The Dude Chart bug?

Hi,

I have an sfp that does at least 300 Mbps rx and 100 Mbps tx.
I made an snmp link that in label shows the correct speed, but in graph it never goes up 100-120 Mbps rx.
Is this a bug or am I doing something wrong? In graph I use builtin Data Source.
Why so much difference between link label and graph?