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.