Ave!
I normally pin my chrome on (Super+1), Editor ( Super+2) and Firefox ( Super+3).
And thanks to this extension https://extensions.gnome.org/extension/413/dash-hotkeys/ i dont regret switching from Windows to Ubuntu.
Before upgrading from 14.10 to 15.04 it worked like this:
Super+1 opens chrome if not opened and focuses if already opened. Super+2 opens chrome if not opened and focuses if already opened. Super+3 opens chrome if not opened and focuses if already opened.
After the update only Chrome ( Super + 1 ) opens always new instance. Firefox and Editor works the same.
Ubuntu Gnome 15.04 with gnome shell 3.16.1, the problems occurs on my Desktop and laptop.