GPS icon always on (even in airplane mode)

Hello,

on my iPhone 5 (os 8.1.3 - 12B466) there is, since two days ago, the GPS icon always on. At the beginning I tried to shut down all the active apps but nothing happened.

Then, I put the phone in "airplane mode" but the GPS icon was still on (and still it is now).

Of course shutting down the phone is useless. Strange is the fact that this behaviour has not begun after an os update, nor after having installed a new app.

I'm going to surrender....any clue?

Thanks