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
record = self.browse(cr, uid, ids[0], context=context)
        if 'kanban_state' in init_values and record.kanban_state == 'blocked':
            return 'project_issue.mt_issue_blocked'
        elif 'kanban_state' in init_values and record.kanban_state == 'done':
            return 'project_issue.mt_issue_ready'
        elif 'user_id' in init_values and record.user_id:  # as
            return 'project_issue.mt_issue_new'
        elif 'stage_id' in init_values and record.stage_id and record.stage_id.sequence <= 1:  # st
            return 'project_issue.mt_issue_new'
        elif 'stage_id' in init_values:
            return 'project_issue.mt_issue_stage'
        return super(project_issue, self)._track_subtype(cr, uid, ids, init_values, context=context)
    def _notification_group_recipients(self, cr, uid, ids, message, recipients, done_ids, group_data, context=None):
        """ Override the mail.thread method to handle project users and officers
        recipients. Indeed those will have specific action in their notification
        emails: creating tasks, assigning it. """
        group_project_user = self.pool['ir.model.data'].xmlid_to_res_id(cr, uid, 'project.group_project_user')
        group_user = self.pool['ir.model.data'].xmlid_to_res_id(cr, uid, 'base.group_user')
        for recipient in recipients:
            if recipient.id in done_ids:
                continue
            if recipient.user_ids and group_project_user in recipient.user_ids[0].groups_id.ids:
                group_data['group_project_user'] |= recipient
            elif not recipient.user_ids:
                group_data['partner'] |= recipient
            else:
                group_data['user'] |= recipient
            done_ids.add(recipient.id)
        return super(project_issue, self)._notification_group_recipients(cr, uid, ids, message, recipients, done_ids, group_data, context=context)
    def _notification_get_recipient_groups(self, cr, uid, ids, message, recipients, context=None):