This happens on both versions Project 98 SR-01 and 2000. To reproduce this
behavior make this.
a) On Gantt Chart or Tracking Gantt view create a task, for instance, of 5
working days and make it Fixed Work task type.
b) Create a resource.
c) Add the resource to the task. There will be 40 hours of work.
d) Now remove the resource. Go to the Task usage view and the 40 hours will
still be there. You can check it on any task oriented view, but it does not
appear on resource oriented views. You can check even on Project Statistics.
If you created the resource with cost, the cost will also remain.
It does not happen with Fixed Duration or Units task type.
So careful when removing resources from a Fixed Work task type.