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
required=True),
        'email_from': fields.char('Email', size=128, help="These people will receive email.", select=1),
        'email_cc': fields.char('Watchers Emails', size=256, help="These email addresses will be added to the CC field of all inbound and outbound emails for this record before being sent. Separate multiple email addresses with a comma"),
        'date_open': fields.datetime('Assigned', readonly=True, select=True),
        # Pr
        'date_closed': fields.datetime('Closed', readonly=True, select=True),
        'date': fields.datetime('Date'),
        'date_last_stage_update': fields.datetime('Last Stage Update', select=True),
        'channel': fields.char('Channel', help="Communication channel."),
        'tag_ids': fields.many2many('project.tags', string='Tags'),
        'priority': fields.selection([('0','Low'), ('1','Normal'), ('2','High')], 'Priority', select=True),
        'stage_id': fields.many2one ('project.task.type', 'Stage',
                        track_visibility='onchange', select=True,
                        domain="[('project_ids', '=', project_id)]", copy=False),
        'project_id': fields.many2one('project.project', 'Project', track_visibility='onchange', select=True),
        'duration': fields.float('Duration'),
        'task_id': fields.many2one('project.task', 'Task', domain="[('project_id','=',project_id)]",
            help="You can link this issue to an existing task or directly create a new one from here"),
        'day_open': fields.function(_compute_day, string='Days to Assign',
                                    multi='compute_day', type="float",
                                    store={'project.issue': (lambda self, cr, uid, ids, c={}: ids, ['date_open'], 10)},
                                    groups='base.group_user'),
        'day_close': fields.function(_compute_day, string='Days to Close',
                                     multi='compute_day', type="float",
                                     store={'project.issue': (lambda self, cr, uid, ids, c={}: ids, ['date_closed'], 10)},
                                     groups='base.group_user'),
        'user_id': fields.many2one('res.users', 'Assigned to', required=False, select=1, track_visibility='onchange'),
        'working_hours_open': fields.function(_compute_day, string='Working Hours to assign the Issue',
                                              multi='compute_day', type="float",
                                              store={'project.issue': (lambda self, cr, uid, ids, c={}: ids, ['date_open'], 10)},