Hello Nicolas ,i don't know how to sort many2many field i'm working to solve that ,but have you used 

the _order in your class to chose with which field your records will be sorted 

class YourClass(models.Model):

_name = 'your.class'

_order = 'date_release desc, name'

name = fields.Char('Title', required=True)

date_release = fields.Date('Release Date')

 this will sort the records first by default from newer to older and then by title

Hi Nicolas,

in my Odoo V8 installation this works. I tested in the products > List view > Click on the header Name it will sort me the results.

Where do you experience this problem ?

Thanks