This is on (an old) single-core a Win2003 box. I noticed that, under Task Manager>Performance, CPU usage was topping out at 80% but under Processes the Idle process is showing around 60-70%, with dips and spikes, of course. Quite odd.
It is not normal.
I recently ran into a situation where the task manager was not correctly showing the additional cores of a multi-core configuration. A chkdsk revealed errors. Correcting the disk/file structure errors corrected the core mismatch situation.
What you are seeing may be something malfunctioning at the OS/application level vs. an actual utilization situation.