In your JMX console, click
and execute the displayClassInfo() method, passing it the fqn of your class.
That may give you some clues as to whether it's being loaded, and where from, and by what.
Thanks for the reply. I did as you suggested and found references to another copy of the jar lingering in my war file (where I'd put it when I'd gotten to the try-everything-regardless-of-whether-it-makes-sense stage of debugging).
Having removed that, the class is being loaded successfully... although now I'm getting Axis-related exceptions - definitely progress though!