What causes very unequal CPU usage?

Is it ever normal for the CPU performance as displayed in the
performance tab of the task manager to be very unequal?

After a time, the CPU usage graph in the performance tab of the task
manager becomes skewed. The CPU in the left graph has a baseline of
about 40%, and the baseline for the one on the right is near 0%. Once
this happens, even if I quit the main program (Retrospect), the shifted
difference between the two CPUs remains. The graph of right CPU does
show usage (fluctuations in the graph), so it's not as if the second CPU
is not being utilized at all.

This is happening on an Arima HDAMA board with dual 248 Opterons and 2
GB RAM using default BIOS settings. The OS is Windows Server 2003
standard edition (32-bit). The major program running is Dantz Retrospect.