So what does this mean? Well PowerMock prepares and loads mocked classes using its MockClassLoader. In some cases this behaviour is undesirable and the mocked class must be loaded by the system class loader instead. This is easily done with the PowerMockIgnore annotation like this...
So in my case since the LinkageError was for the javax/management/MBeanServer class, I use the "javax.management.*" value to make sure that everything in the javax.management package is deferred to the system class loader (I could have used the specific class but I chose to use the entire package).
There is a way to apply this type of configuration globally by creating a file, "org/powermock/extensions/configuration.properties", and adding it to the classpath (if using Maven in the src/test/resources directory). The configuration file is a standard Java Properties file and needs to have the "powermock.global-ignore" set the same way as the annotation, however I couldn't get this to work.