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.

_inherit = "project.project"
    def _get_alias_models(self, cr, uid, context=None):
        res = super(project, self)._get_alias_models(cr, uid, context=context)
        res.append(("project.issue", "Issues"))
        return res
    def _issue_count(self, cr, uid, ids, field_name, arg, context=None):
        Issue = self.pool['project.issue']
        return {
            project_id: Issue.search_count(cr,uid, [('project_id', '=', project_id), ('stage_id.fold', '=', False)], context=context)
            for project_id in ids
        }
    def _issue_needaction_count(self, cr, uid, ids, field_name, arg, context=None):
        Issue = self.pool['project.issue']
        res = dict.fromkeys(ids, 0)
        projects = Issue.read_group(cr, uid, [('project_id', 'in', ids), ('message_needaction', '=', True)], ['project_id'], ['project_id'], context=context)
        res.update({project['project_id'][0]: int(project['project_id_count']) for project in projects})
        return res
    _columns = {
        'issue_count': fields.function(_issue_count, type='integer', string="Issues",),
        'issue_ids': fields.one2many('project.issue', 'project_id', string="Issues",
                                    domain=[('stage_id.fold', '=', False)]),
        'issue_needaction_count': fields.function(_issue_needaction_count, type='integer', string="Issues",),
    }
    @api.multi
    def write(self, vals):