Error while trying to make a refund

I have made an order and did the whole process of delivering the articles and making an invoice.

Now I go to the invoice which has been paid. On top of the screen is a button "Refund Invoice".

When I click on it, a small screen appears to get some information from the user. As reason I type "Manco" (without quotes) and click on "Create Refund".

This generates the following error:

    OpenERP Server Error

    Client Traceback (most recent call last):

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/http.py", line 203, in dispatch

    response["result"] = method(self, **self.params)

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py", line 1133, in call_button

    action = self._call_kw(req, model, method, args, {})

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py", line 1121, in _call_kw

    return getattr(req.session.model(model), method)(args, *kwargs)

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 43, in proxy

    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 31, in proxy_method

    result = self.session.send(self.service_name, method, *args)

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 104, in send

    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)

    Server Traceback (most recent call last):

    File "/usr/lib/pymodules/python2.7/openerp/addons/web/session.py", line 90, in send

    return openerp.netsvc.dispatch_rpc(service_name, method, args)

    File "/usr/lib/pymodules/python2.7/openerp/netsvc.py", line 293, in dispatch_rpc

    result = ExportService.getService(service_name).dispatch(method, params)

    File "/usr/lib/pymodules/python2.7/openerp/service/web_services.py", line 626, in dispatch

    res = fn(db, uid, *params)

    File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 188, in execute_kw

    return self.execute(db, uid, obj, method, args, *kw or {})

    File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 131, in wrapper

    return f(self, dbname, args, *kwargs)

    File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 197, in execute

    res = self.execute_cr(cr, uid, obj, method, args, *kw)

    File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 185, in execute_cr

    return getattr(object, method)(cr, uid, args, *kw)

    File "/usr/lib/pymodules/python2.7/openerp/addons/account/wizard/account_invoice_refund.py", line 223, in invoice_refund

    return self.compute_refund(cr, uid, ids, data_refund, context=context)

    File "/usr/lib/pymodules/python2.7/openerp/addons/account/wizard/account_invoice_refund.py", line 149, in compute_refund

    refund_id = inv_obj.refund(cr, uid, [inv.id], date, period, description, journal_id, context=context)

    File "/usr/lib/pymodules/python2.7/openerp/addons/account/account_invoice.py", line 1233, in refund

    context=context)

    File "/usr/lib/pymodules/python2.7/openerp/addons/account/account_invoice.py", line 1197, in _prepare_refund

    invoice_lines = self._refund_cleanup_lines(cr, uid, invoice.invoice_line, context=context)

    TypeError: _refund_cleanup_lines() got an unexpected keyword argument 'context'

I have installed the latest version of V7 from nightly.openerp.com/7.0/nightly/deb/ ./

I am using Ubuntu 12.04.2, 64 bit.