Your right-somethings not right, and replacing the parts is where i'm starting-plus my new knowledge you guys have supplied.
The only way i can explain is that the washer was riding squarely on the bushing flange after torqueing, because the sleeve is worn and undersized now. The large area of the washer is enough to hold the bushing which is leveraged by the LCA and loosen the nut.Once everything is loose, the nut doesn't loosen any further.