This issue has been occurring on my phone for months. I have a suspicion that it's connected to the application App Manager 3. If the OP has App Manager 3 installed, perhaps this suspicion will be corroborated. The fault happens (on my phone) sporadically, and I correct it by using the backup and restore function included in Nova Prime. As it is nothing more than a minor annoyance, I haven't looked any further into it.