It could be normal. Was the ride new when you got it? If so, it is possible that those particular gears are weak in your ride...or that you got a bad batch. Some new RCs do not have the best diff gears and a powerful engine ends up damaging the drive train.
If you were not tormenting the RC, ie driving in high grass, thick mud, etc., then odds are you simply have a new RC with weak diffs. Happens.
Buy replacement gears, build up the diffs, look for upgrades to come out or mods to be posted that might prevent this from happening again. Welcome to the wonderful world of Nitro RC.