after changing the signature of a method in an interface the java module 
recognized it, and even suggested the right synchronization.
the code through was not changed after I clicked on the "process all" button.

to reconstruct(example):
1. add the following interface:
public interface A {
    public void func();
}
2. add the following class:
public class B implements A{
    public void func() {}
}
3. change A to :
public interface A {
    public int func();
}
4. after the synchronization dialog appears click on the "process all" button, 
or select the change from the list and click on the "process" button.

results: the code of B does not change.

note: passed arguments are still updated.
found on 3.2 release (b39)