Comment 4 for bug 923805

Tried reproducing, no issue there: added a button@type=object to a view, calling into a handler method whose body is just the following:

    return {
            'type': 'ir.actions.act_window',
            'view_mode': 'tree',
            'res_model': some_model
    }

the list opens rapidly and without issues.

Don't hesitate reopening the bug or opening a new one with more information or a repro case (a minimal openerp module exposing the issue for instance), but for now I'm closing it as invalid as what you describe seems to work with no issue.