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.

calendar_id = issue.project_id.resource_calendar_id.id
            dt_create_date = datetime.strptime(issue.create_date, DEFAULT_SERVER_DATETIME_FORMAT)
            if issue.date_open:
                dt_date_open = datetime.strptime(issue.date_open, DEFAULT_SERVER_DATETIME_FORMAT)
                values['day_open'] = (dt_date_open - dt_create_date).total_seconds() / (24.0 * 3600)
                values['working_hours_open'] = Calendar._interval_hours_get(
                    cr, uid, calendar_id, dt_create_date, dt_date_open,
                    timezone_from_uid=issue.user_id.id or uid,
                    exclude_leaves=False, context=context)
            if issue.date_closed:
                dt_date_closed = datetime.strptime(issue.date_closed, DEFAULT_SERVER_DATETIME_FORMAT)
                values['day_close'] = (dt_date_closed - dt_create_date).total_seconds() / (24.0 * 3600)
                values['working_hours_close'] = Calendar._interval_hours_get(
                    cr, uid, calendar_id, dt_create_date, dt_date_closed,
                    timezone_from_uid=issue.user_id.id or uid,
                    exclude_leaves=False, context=context)
            days_since_creation = datetime.today() - dt_create_date
            values['days_since_creation'] = days_since_creation.days
            if issue.date_action_last:
                inactive_days = datetime.today() - datetime.strptime(issue.date_action_last, DEFAULT_SERVER_DATETIME_FORMAT)
            elif issue.date_last_stage_update:
                inactive_days = datetime.today() - datetime.strptime(issue.date_last_stage_update, DEFAULT_SERVER_DATETIME_FORMAT)
            else:
                inactive_days = datetime.today() - datetime.strptime(issue.create_date, DEFAULT_SERVER_DATETIME_FORMAT)
            values['inactivity_days'] = inactive_days.days
            # fi
            for field in fields:
                res[issue.id][field] = values[field]
        return res
    def on_change_project(self, cr, uid, ids, project_id, context=None):