Custom data source

Dear All, I have a problem probably connectd with RRD and how it was defined but don't know how to change this. I have data source based on ssh script that produce the following output:

OK|attempts=8529 accept=5686 reject=2843

Data pionts type is defined as DERIVE.

The thing that I don't understand is how zenoss writes data that it gets from script to rrd file. The following lines shows consecutive script ouptuts with timestamp:

Wed, 25 Feb 2015, 13:48:23 CET OK|attempts=8528 accept=5685 reject=2843
Wed, 25 Feb 2015, 13:53:23 CET OK|attempts=8528 accept=5686 reject=2843
Wed, 25 Feb 2015, 13:58:23 CET OK|attempts=8529 accept=5686 reject=2843
Wed, 25 Feb 2015, 14:01:14 CET OK|attempts=8529 accept=5686 reject=2843
Wed, 25 Feb 2015, 14:06:13 CET OK|attempts=8529 accept=5686 reject=2843

And now dump from RRD that stores attempts datapoint:

0.0000000000e+00
0.0000000000e+00
1.0777777778e-03
2.2555555556e-03
0.0000000000e+00

As you can see the change between attempts=8528 and attempts=8529 is distributed among two samples in RRD. Why this hapens and how can I solve this

Would be very grateful if someone could help :)

Best regards, Andrzej