Hello,
I just did an erase and clean install of El Capitan, before I did that I smart updated two bootable clones. When I'm in El Capitan, the Clones mount OK and I can access all the files.
However if I attempt to boot from them, instead of the usual log in screen with a few users, I get only a Guest User and another User with no name, see screenshot below.
Both bootable clones are doing this. I have another mac that is still running Yosemite but I am getting the same result with that too, which surprised me as I thought it must have something to do with El Capitan. Both the smart updated clones were made with v2.8
Thanks