The sheer water weight of eating carbs again after VLCD like Cambridge can cause up to 7lbs in weight gain, but its not true weight, its water,
For you to have lost 1/2 a lb, and then maintain for 2 weeks afterwards is actually very impressive. It is your body adjusting to the additional carbs, salt etc that's in "normal" food, its why when you have finished with the shakes on CD you work up the plans, its a) to re-educate you into a healthy eating pattern and b) minimise the carb/water gain, bearing in mind that glycogen binds to 3 times its own weight in water.
Don't worry, your body will settle down shortly and get into its own way of working again.