Today (27 April, 2013), a new app named 'ssLauncher starter' has been released on Google Play. You can resolve this issue with this application.
1. install 'ssLauncher starter' from Google Play. link here
2. press home button.
3. select 'ssLauncher starter' and 'Always'
Now you can ignore the below. :)
Now ssLauncher the Original (paid version) has an issue that default launcher setting is reset when rebooting the device.
This issue occurs only when satisfying the following conditions.
1. ssLauncher the Original (paid version) on Android 4.1.x: The other Android version, even 4.2, is okay.
2. Important! Only when installed or updated from Google Play Store: It does not happen when the apk is installed manually.