Tak to vypada, ze jsem to vygoogloval zatim to funguje (od vcerejsi půlnocí):
http://forums.androidcentral.com/samsung-galaxy-s4/334381-touchwiz-wont-stay-default-launcher.html
Guys, I MIGHT HAVE FOUND THE SOLUTION.
Uninstall the latest search for Google Search (11/15/2013) - It is very unstable. When you hit the Google search bar and then the home button on some your Android devices, it will prompt you for the zillionth time "continue using action as..." where you'll have to select a launcher. I just uninstalled the latest update and it fixed it for me (at least for the time being). No more prompts - Touchwiz is stored as default launcher.