Motorola Moto G 4G — Moto G 3rd Gen phone in vibrator mode

Hello,

I have Moto G 3rd Gen phone brought last week,
when the phone is in vibrator mode and the screen lock is on, when we get incoming call, the phone vibrates only once and goes to silence even though the call is still coming

Is there any settings thats need to be made, or is this the drawback of this phone,

I used earlier Moto G 2nd gen phone and didnt face this problem in that

please suggest

Thanks
Srinath N