Nimbus: ClassCastException when running with MultiLookAndFeel

When using Nimbus with MultiLookAndFeel (triggered by adding an Axiliary L&F), a ClassCastException is thrown. Presumably, Nimbus is not aware of MultiLookAndFeel.

Sample code to reproduce the bug is available at:
http://www.pbjar.org/Nimbus/NimbusBug.jar
(attached)

It contains source code and the compiled class files and is a runnable jar file.

Steps to reproduce the problem:
- Install Java 6uN Early Access.
- Run bug.nimbus.BugSample (or execute the jar file) and select the Nimbus L&F from the menu.