I have installed many desktop environments on my debian8.1 such as cinnamon, mate, lxde, xfce.  I found that I can't select the desktop as I like ,whichever I choose, the desktop is always mate when to login in my debian8.1.It is no use to choose lxde in the menu, I have tested it many times and other desktop such as cinnamon.How to change the default setting to make mate as default desktop environment?
Why can't change my destktop from mate into others?
debian;desktop environment;cinnamon;lxde;mate