#4 JRobin does not calculate average properly sometimes

[Anonymous]

We use JRobin (version 1.5.4) to store SNMP counters and produce graphs. We have configured JRobin to archive everyday, every week, every month and year for AVERGAE and LAST.
Below is the detail of RRD paramters :-
Step :- 30
HeartBeat :- 300
Type :- GAUGE

Sometimes JRobin stores wrong value. This is not a regular behavior but only occurs seldom.
Please suggest what can be the issue, I have confirmed that my application sends the correct value to Sample.update method.