In the code of TreeSelection.c there's a global reference being created:

fedata->obj = (*env)->NewGlobalRef(env, connect_to);

But apparently there's no calling to DeleteGlobalRef(). That means the GC won't
be able to collect the object referenced by fedata->obj, because it "thinks"
there's still someone referencing it
(http://www.science.uva.nl/ict/ossdocs/java/tutorial/native1.1/implementing/refs.html).

There are 2 solutions:
   1) call DeleteGlobalRef() somewhere
   2) Make a Weak global reference instead of a global reference
(http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-12.html#weakrefs)

I think option 2 might be the best way.