I can set Nova Launcher as default launcher in Settings -> Installed Apps -> Defaults -> Launcher, but whenever I tap the home button, the device loads the system launcher. In the settings of Nova Launcher I keep getting the following message: "Not set as default - Nova launcher is not set as the default launcher. Tap to set."
I tried all combinations of rebooting / re-installing / clearing caches and whatnot. It all doesn't help.