Dict in binary pickle causes exception

[greg]

When I try to unpickle a pickle containing a dictionary
that was written in binary format, I get the following
exception:

   TypeError: dict objects are unhashable

The same thing happens whether I use pickle or cPickle
to do the unpickling.

Is this a known limitation, or a bug? The non-binary
format handles dictionaries just fine, and I don't
see why the format should make a difference to what
is picklable. Also, I can't find any mention in the
documentation about any additional restrictions when
using the binary format.

I'm using MacPython 2.2.

Greg