More than one coder for gwt autobean causes AssertionError

When deserializing an autobean from JSON I get an AssertionError from com.google.web.bindery.autobean.shared.impl.AutoBeanCodexImpl.CoderCreator#getCoder. Looks like there are two types registered for my autobeans:

• my.project.model.MyAutoBean
• java.lang.Class

Of course I find the second one quite useless but I don't know where it comes from and how to get rid of it. When I disable assertions the code just works fine and (de)serializes my Autobean perfectly.

I already get two types in the initialization of the ClientPropertyContext but I cannot debug what in MyAutoBean.traverseProperties is happening.