I had the same problem the last week.
I received a call while having my phone on vibration (without ringing), and as soon as I accept the call, the vibration stuck on until I end the call!
It was pretty weird trying to make a serious conversation with vibration at full speed
But that only happened to me once.. (I have this phone 3 months)
If your problem persist, definitely contact Microsoft-Nokia.
About a month or two ago I had the same issue.. Happened weeks after I bought it.. And it stopped after turning it off and happened a couple times more but then never happened again so don't know why can that happen
Enviado desde mi Windows Phone usando Tapatalk
Happened to me a few times too, and I just bought it 2 months ago. Stops after a minute or two, and happens randomly. Not sure why and how to fix this =/
This has happened 2 or 3 times on my 635 in the last couple of weeks. Have to either remove the battery or soft reset to clear. I never have my phone on vibrate, but some random notification triggers the motor and it won't stop until the phone is shut off.