I'm getting these results on both:
Python 3.2.3 (default, Apr 10 2013, 06:11:55)
[GCC 4.6.3] on linux2
and
Python 2.7.3 (default, Apr 10 2013, 06:20:15)
[GCC 4.6.3] on linux2

The symptoms are exactly as Terrence described.

Nesting proxied containers is supposed to be a supported use case! From the documentation: http://docs.python.org/2/library/multiprocessing.html#proxy-objects

>>> a = manager.list()
>>> b = manager.list()
>>> a.append(b)         # referent of a now contains referent of b
>>> print a, b
[[]] []
>>> b.append('hello')
>>> print a, b
[['hello']] ['hello']

The documented code works as expected, but:
>>> a[0].append('world')  # Appends to b?
>>> print a, b
[['hello']] ['hello']

I've attached my reproduction as a script.