Why is my S4 rebooting when i turn wifi off?

[AC Question]

Hi. Every time I am connected via wifi at home or anywhere else, and decide to switch off the wifi setting on my S4, it reboots once. It started acting this way since the OS upgrade to Lollipop last Summer.
The only way it doesn't restart, is when switch on the airplane mode. In this case, it turns off all communication (including wifi of course) without restarting. Any help? Thank you.