Error reading document after multipart put

GETing a document after a multipart PUT which uploaded an attachment generates a 500 error. To reproduce:

Following document is in a DB (called semo_test here).

{ "_id": "doc0", "_rev": "1-7e97409c987eac3a99385a17ad4cbabe", "value": 0 }

Update the document and add an attachment using a multipart/related request:

PUT /semo_test/doc0 HTTP/1.1
Accept: application/json, /
content-type:
multipart/related;boundary=multipart_related_boundary~~~~~~~~~~~~~~~~~~~~
Host: localhost:5984
Content-Length: 435
Connection: keep-alive

--multipart_related_boundary~~~~~~~~~~~~~~~~~~~~
Content-Type: application/json

{"value":0,"_id":"doc0","_rev":"1-7e97409c987eac3a99385a17ad4cbabe","_attachments":{"plus
1":{"stub":false,"follows":true,"content_type":"application/json","length":14}},".cache":{"plus
1":

{"timestamp":"2012-08-13T13:59:27.826Z"}

}}
--multipart_related_boundary~~~~~~~~~~~~~~~~~~~~

{"value":"01"}

-multipart_related_boundary~~~~~~~~~~~~~~~~~~~~-
HTTP/1.1 201 Created
Server: CouchDB/1.2.0 (Erlang OTP/R15B)
Location: http://127.0.0.1:2222/semo_test/doc0
ETag: "2-37f62cdf8cb68339a30b7b20d7eb0d1d"
Date: Mon, 13 Aug 2012 14:00:49 GMT
Content-Type: application/json
Content-Length: 67
Cache-Control: must-revalidate

{"ok":true,"id":"doc0","rev":"2-37f62cdf8cb68339a30b7b20d7eb0d1d"}

Request the updated document:

GET /semo_test/doc0 HTTP/1.1
Accept: application/json, /
Host: localhost:5984

HTTP/1.1 500 Internal Server Error
Server: CouchDB/1.2.0 (Erlang OTP/R15B)
Date: Mon, 13 Aug 2012 14:10:02 GMT
Content-Type: application/json
Content-Length: 43
Cache-Control: must-revalidate

{"error":"unknown_error","reason":"undef"}

Following stacktrace is generated when handling the GET:

[Mon, 13 Aug 2012 14:10:02 GMT] [error] [<0.6811.10>] Uncaught error
in HTTP request:

{error,undef}

[Mon, 13 Aug 2012 14:10:02 GMT] [info] [<0.6811.10>] Stacktrace:
[

{base64,encode, [<<115,176,77,34,80,64,240,8,14,182,224, 181,170,42,191,128>>], []}

,
{couch_doc,'to_json_attachments/4-fun-0',
4,
[

{file,"couch_doc.erl"},{line,110}]},
{lists,map,2,
[{file,"lists.erl"},{line,1173}]},
{couch_doc,to_json_attachments,4,
[{file,"couch_doc.erl"}

,

{line,101}

]},
{couch_doc,doc_to_json_obj,2,
[

{file,"couch_doc.erl"}

,

{line,153}

]},
{couch_httpd_db,send_doc_efficiently,4,
[

{file,"couch_httpd_db.erl"},
{line,836}]},
{couch_httpd_db,do_db_req,2,
[{file,"couch_httpd_db.erl"}

,

{line,230}

]},
{couch_httpd,handle_request_int,5,
[

{file,"couch_httpd.erl"}

,

{line,317}

]}]
[Mon, 13 Aug 2012 14:10:02 GMT] [error] [<0.6811.10>] Uncaught
server error: undef
[Mon, 13 Aug 2012 14:10:02 GMT] [info] [<0.6811.10>] 127.0.0.1 - -
GET /test/doc0 500

(This problem was originally reported on user@couchdb and Robert Newson requested that I raise it here. Note that these steps generate the error as described when I test on one couchdb installation, but when I try the same steps on a separate installation - also Mac OS 10 - the 500 error doesn't occur, so possibly the error is somehow related to db state).