"Minimise Class icons in diagrams. If enabled, then the attributes and operations compartiments will not be shown in the classes on the generated class diagrams. Note: This item is checked by default, and is overseen by many users, which are then surprised by the result."
So something is enabled by default that surprises many users? That doesn't strike me as good interface design. Anyway, thanks to a bit of googling and this forum post I figured it out.
I've only got a simple Java app and really didn't want to have to install Netbeans or Eclipse just to generate a Class Diagram, so I'm glad I got ArgoUML out figured.