I had an incorrect understanding of the UIMA model for this, and confused an instance of Resource with an instance of its implementation.
A Resource in UIMA is an Interface implemented by framework code parts that are specializations for the many kinds of resources managed by UIMA. These resources are created from Resource Specifiers using produceResource. One aspect of Resource instances is that they contain a reference to an "implementation" - another Java class, which is *not* an instance of Resource. This aspect is only present in some kinds of resources. For External Resources, the descriptor for this, and its internal Java class (ExternalResourceDescription) have an element, "implementationName", which is name of the Java class implementing the resource. This class doesn't implement the Resource API. I incorrectly switched several parts of ResourceManager_impl from Object to Resource based on my misunderstanding, and will now revert that. -Marshall
