PUTing JSON with invalid UTF-8 returns no error message

I'm reading utf-8 documents from disk and embedding them in a json structure. Several of them contain invalid utf-8 characters. If I PUT to couchdb I get a stack trace in my debug log and the tcp connection is dropped--no http code is returned

[Wed, 08 Feb 2012 17:58:55 GMT] [error] [<0.28906.4>] {error_report,<0.31.0>,
{<0.28906.4>,crash_report,
[[{initial_call,
{mochiweb_acceptor,init,
['Argument__1','Argument__2','Argument__3']}},

{pid,<0.28906.4>}

,

{registered_name,[]}

,
{error_info,
{exit,
{ucs,{bad_utf8_character_code}},
[{xmerl_ucs,from_utf8,1,
[

{file,"xmerl_ucs.erl"}

,

{line,185}

]},
{mochijson2,json_encode_string,2,
[

{file,"mochijson2.erl"},{line,148}]},
{mochijson2,'json_encode_proplist/2-fun-0',3,
[{file,"mochijson2.erl"}

,

{line,129}

]},
{lists,foldl,3,[

{file,"lists.erl"}

,

{line,1197}

]},
{mochijson2,json_encode_proplist,2,
[

{file,"mochijson2.erl"}

,

{line,132}

]},
{couch_httpd,send_json,4,
[

{file,"couch_httpd.erl"},{line,635}]},
{couch_httpd,handle_request_int,5,
[{file,"couch_httpd.erl"}

,

{line,272}

]},
{mochiweb_http,headers,5,
[

{file,"mochiweb_http.erl"}

,

{line,126}

]}]}},

{ancestors, [couch_httpd,couch_secondary_services, couch_server_sup,<0.32.0>]}

,

{messages,[]}

,

{links,[<0.113.0>,#Port<0.30990>]}

,
{dictionary,
[{mochiweb_request_body,
<<"

{\"id\":111,\"doc\":\"ker\\u0019 u\"}

\n">>},

{mochiweb_request_qs,[]}

,

{mochiweb_request_recv,true}

,

{jsonp,no_jsonp}

,

{mochiweb_request_cookie,[]}

]},

{trap_exit,false}

,

{status,running}

,

{heap_size,2584}

,

{stack_size,24}

,

{reductions,7048}

],
[]]}}