[binary] [trunk/6.1]saving a binary field not saved yet crashes

observed in latest 6.1, server 4199 addons 6934 web 2353

To reproduce:

install document
documents -> create
file content: select a file
(don't save)
press "save as"

2012-06-08 13:23:08,892 56381 ERROR ? openerp.addons.web.common.http.HttpRequest.dispatch: An error occurred while handling a json request
Traceback (most recent call last):
  File "/Users/leo/workspace/oe61/server/openerp/addons/web/common/http.py", line 260, in dispatch
    r = method(controller, self, **self.params)
  File "/Users/leo/workspace/oe61/server/openerp/addons/web/controllers/main.py", line 1451, in saveas_ajax
    (field, model, id))
ValueError: No content found for field 'datas' on 'ir.attachment:'

All is fine with the gtk client, but that happens with other binary fields in other modules. So I think this is a problem with the webclient, not with the document module.

Thanks!