Sean,

In addition to the answers already given here's another one to consider:  Plastisol rack coatings, depending on the age of the bulk plastisol used in the coating process, can actually be conductive.  If you consider that the bulk plastisol builds up with metallics over time it's understandable.  When HP built and plated boards I participated in a study to pinpoint the cause of racks plating up, especially newly coated ones.  It was discovered that the rack coater was using old plastisol and had discovered a wrench, and some nuts and bolts in the bottom of the plastisol tank.  Fresh plastisol solved the plate up problem.