Around the time I fresh installed Ubuntu 12.04, I noticed that I can start multiple instances of Emacs. I find this annoying because I will think that a buffer should be open, but I'm in the wrong Emacs window. I may have changed something in .emacs, but I really don't think I did. I also reverted all of my customizations that are stored in ~/.emacs.d/custom.el. Emacs previously would give some error about another emacs server being open when I would attempt to start an additional instance of it, but it no longer does this. Any ideas on how to restore this behavior?