Right now the XStream serializer used in Confluence is configured to use a delegating classloader that only delegates to the PluginsClassLoader. This causes ClassNotFoundExceptions when trying to deserialize an instance of a class which is not part of a plugin. It starts working though as soon as a StaticPlugin is loaded, because StaticPlugins use the application class loader (which is a really bad side effect).
We should use a class loader that tries the application class loader first and then the plugins class loader.