Impacted versions:
9.0 Community & 9.0 Enterprise

Steps to reproduce:
- Open up a V9 runbot
- Go to projects and click on the issues item, for example for the project 'Research & Development':
  ![image](https://cloud.githubusercontent.com/assets/6352350/13873686/65f2c31c-ecf3-11e5-917a-38df2832bd00.png)
- The project tasks view is opened in place of the project issues. (notice that this only happens every once in a while, about once in five attempts) Example:
  ![image](https://cloud.githubusercontent.com/assets/6352350/13873789/14798b64-ecf4-11e5-9b77-f2ad5d3a8adc.png)

Current behavior:
Every once in a while (about one out of five attempts) after clicking on the issues button it will open up the project tasks, not the issues.

Expected behavior:
When you click on the issues the view with all issues opens, not the view for all tasks.

import calendar
from datetime import datetime,date
from dateutil import relativedelta
import json
import time
from openerp import api
from openerp import SUPERUSER_ID
from openerp import tools
from openerp.osv import fields, osv, orm
from openerp.tools import DEFAULT_SERVER_DATETIME_FORMAT
from openerp.tools import html2plaintext
from openerp.tools.translate import _
from openerp.exceptions import UserError, AccessError
class project_issue(osv.Model):
    _name = "project.issue"
    _description = "Project Issue"
    _order = "priority desc, create_date desc"
    _inherit = ['mail.thread', 'ir.needaction_mixin']
    _mail_post_access = 'read'
    def _get_default_partner(self, cr, uid, context=None):
        if context is None:
            context = {}
        if 'default_project_id' in context:
            project = self.pool.get('project.project').browse(cr, uid, context['default_project_id'], context=context)
            if project and project.partner_id:
                return project.partner_id.id
        return False
    def _get_default_stage_id(self, cr, uid, context=None):