Jackson question... why does this fail?

<dataFormats>
<json id="jack" library="Jackson"/>
</dataFormats>
...
<route id="myRoute">
<from ref="listener" /> // mina component
<unmarshal ref="jack" /> // unmarshal it
<marshal ref="jack" /> // marshal it
</route>

I can put a bean:myBean in between and see that, yes, it is being
unmarshalled correctly. Even more complex JSON will unmarshall correctly,
and I can traverse the returned Map.

{"a":5} // input
[B [ at ] 73207f36 // output

Why does the <marshal/> call return crap (an object ref of some kind?) even
for simple calls?

Thanks,

-mox