Maybe your dependent jar is loaded before the other jar file. Try having a depends clause in ur jboss.xml of the middle-man bean.
Or pack your dependent jar(the middle-man) as an ear. JBoss by default loads all the jars and then the ears. So by the time it gets to your middle-man, the other bean would have been loaded.
The unit test may not give you an accurate picture as you cannot really find out if the dependent jar got loaded before/after the other bean.
Further research has shown me that I have a more general problem. I cannot successfully create a CMR relationship with beans that are defined in other ejb-jar files. Is this an invalid thing to do?
I have another post I just put up with more details, but I wanted to rename the topic since the problem was more general than an M:N problem.