Hi,
Sorry I didn't see you post until Monday afternoon :-(

The Task Sheet view normally has the Entry table applied - not the Tracking table which has the % complete, actual start, actual finish etc - so that in and of itself is not sign of corruption.

However, wWhat you describe is not normal and I have never known Project to spontaneously set % complete. Is it possible you accidentally hit the Update Project Command? Are the completed tasks in the future? When you are looking at the resource usage view, what you see underneath the resource's name are assignments - not tasks.

If you updated % complete on tasks with multiple resources assigned, Project will automatically update all assignments.

Julie