When I login, my choice of desktop environment doesn't work.
The Ubuntu display manager, lightdm, has this weird bug where your choice of desktop environment is reset when you enter a username. The workaround however is simple.
- Enter your username
- Enter your password, but don't login yet
- Choose your desktop environment
Login in this order and your desktop environment will be loaded and set as the new default, so you will only have to do this once... unless someone else does the same thing with a different desktop on the same PC.