Let's take following case:

• Plugin A defines a sub class of Descriptor (PluginADescriptor)
• Plugin B depending on plugin A defines a Describable class described by an instance of PluginADescriptor (DescribableB).
  • Watch that it is described by an instance of *not a subclass of * PluginADescriptor but PluginADescriptor itself.

This is exactly the case SimpleBuildSelectorDescriptor in copyartifact-plugin.

In this case, the following jelly fails:

<st:include from="${d}" page="${d.configPage}" />

as stapler try to load config.jelly from plugin A, but it's actually in plugin B.

That should be:

<st:include class="${d.klazz}" page="${d.configPage}" />