Somehow my reply mails vanish and do not get 
inserted properly into the messages list of issues.
I'm using 0.4.3 almost vanilla install with extended
template
and the bsddb3 backend and Python 2.1.3.

I've tracked the problem into mailgw.handle_message() 
and the following lines:

            if nodeid:
                # add the message to the node's list
                print "nodeid",nodeid
                print "message_id", message_id
                messages = cl.get(nodeid, 'messages')
                messages.append(message_id)
                props['messages'] = messages

further down:
            if nodeid:
                print "let's set",nodeid,props
                cl.set(nodeid, **props)
                print cl.get(nodeid,"messages")
later 
       # commit the changes to the DB
        self.db.commit()

The printed values are all fine and as expected. 
Still using the admin command (with the same user)
 I can see the value is missing from
"messages". Using the admin command I can easily add
and commit it.
Strange.

Logged In: YES 
user_id=113859

This bug only occurs if the issue.assignedto=None.
Once it is assigned it works.

Logged In: YES 
user_id=6405

The nosy reactor has some code that checks for changes to 
assignedto and modifies the nosy list accordingly. You need to change 
line 144 from: 
 
if newvalues.has_key('assignedto'): 
 
to 
 
if newvalues.has_key('assignedto') and newvalues['assignedto'] is not 
None: