Grouping java classes using doxygen

Question

Am having trouble having the class heirarchy place the classes in the same package under the same node. For some reason currently this is what I get:

|-q.r.s.t 
+-a.b.c.d
|---a.b.c.d.e <---This is a class part of the a.b.c.d package
|-a.b.c.d.f <-- Even though this is also part of the same package this  
                class for some reason appears in its own entry and not under the 
                package header:(

Any tips on what I can do to get my classes organised the way I expect it? The way I expect it:

|-q.r.s.t 
+-a.b.c.d
|---a.b.c.d.e 
|---a.b.c.d.f

The configuration option has been set to optimise for Java. Doxygen version 1.5.8