This is not unusual at all. Your body has been starved for carbohydrates and most likely your stores are at nil. When you ingest carbs on your carb up day your body is going to supercompensate. For all it knows it won't be getting any more carbs so instead of using them for energy they are stored as glycogen in the liver and muscle. Meanwhile your body is still releasing ketones and free fatty acids into the blood stream to support your functions. I have carbed up many times and not left ketosis, when done right. However even if you do it doesn't matter in the long run. Hope this helps.