According to the spec:
"Classes and interfaces mentioned by LoadableDescriptors may optionally be loaded when the referencing class is derived and created (5.3.5), or during early stages of linking (5.4)."

This language opens up the possibility to use non-class LoadableDescriptors as attributes. For example, arrays or primitive integers. Since it "may optionally be loaded", the VM is free to (and currently does) ignore these when preloading. However, such behaviour should be disallowed explicitly and raise a java.lang.ClassFormatError.