JConsole shows negative CPU Usage

While monitoring of CPU Usage jconsole shows negtive CPU Usage.

.csv file and screenshot of such situation are atteched.

How to reproduce:

Start jconsole and attach it to any process(Java2D demo in my case).
Negative cpu usage will be shown on cpu usage monitor afrter some monitoring time.

My Machine:
Processor: Intel(R) Pentium(R) D CPU 3.20GHz x2
OS: Gentoo Linux

On slow machines like P-III(~800 MHz) cpu monotor shows correct values.