CPU meter in Activity Monitor all wrong??

According to the screenshot, both Users (green) and System (red) uses 0,19% CPU each. Which means that idle (black) should be around 99%, which it clearly isn't.

If I check each process individually, none is using more than 1% of CPU.

Does anyone knows why this is?

The screenshot is taken after a reboot and I don't use and third-party background services like VMWare. It's Mac Pro 2.66 Quad (2009).