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.

addons/project_issue/project_issue.py
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):