Got the car back from the dealership. They basically told me that the car was not designed to go over 50Km/h on "L" mode and that the behaviour I am experiencing is normal. I call them on their bull**** answer as this car never had that problem for the past 2 years. They would not listen to me and kept saying it is a normal situation as per GM driving book. At this point I am pretty fed up with GM and the Volt. Don't get me wrong, it is a great car, but the service is a big zero. What should I do now?
Like I said above, drive it in D, use the brake pedal, only use L when trying to slow down on long mountainous hills.
Another situation that comes up often is when you lift in L or even during normal braking, if the drive wheels happen to hit a bump which causes the wheels to go airborne and spin, it will feel like the volt is lurching forward when in reality, it just isn't braking as you'd expect. When my daughter attended grade school, there was a spot that I hit daily which exhibited this behavior, even while in D using the brake pedal. It sends a sinking feeling into your gut as you are expecting the car to stop, and it doesn't for a brief moment, then catches itself. The car actually disengages regen when it detects wheel slippage and if you can catch it, you might even see the traction control or stabilitrak dash lights flash. So I suspect the car is working as designed, there's not much the dealership can do about this (if this is indeed what you are seeing) and you have to not get so upset at the service department for operating the vehicle where you're putting your tires and suspension on edge to cause this.
That's like getting upset that your rear tires are wearing prematurely on a Vette...