My 2010 roadster has always had this issue and I'm not sure if it happens on ALL roadsters or just mine. On a flat road, when I decelerate the regen braking kicks in and you see the Amp gauge swing to charging (OK, that's all pretty much as you would expect). When you do the same thing but go over a bump in the road, the car lurches forward, the regen disengages, the Amp gauge swings to the right and the TC light flicks on for a second. The loss of regen braking makes it feel like the car just accelerated forward. This doesn't sound like its meant to be this way but this is a "basket case" according to Elon Musk, so maybe it's just the way it is. I've tried disabling TC but it has no effect.