Yeah, two people use one of my machines, which is set to not log in automatically to AB. I'll call them Fred and Bill.
Now, Bill goes to AB, clicks Sign in and finds Fred's name already there. He erases Fred's name and types in "Bill", then enters his password. Up pops AB with "Welcome back Fred". He has to close the browser and repeat the operation a number of times before AB will actually log him in as Bill.