going off med~cause more seizures????

My 2 year old has been on depakote for about 1 year. After talking to the neuro, we decided to switch him to lamictal, even though the depakote was working pretty well. We wanted to switch him due to the lower side effects and less monitoring. Here is my question: He was taking four, 125 mg sprinkles twice a day, then we went down to 3.5 for two weeks, 3 for 2 weeks, 2.5 for two weeks, etc, going down a half a capsule every two weeks. During this time we were watching his levels closly and bringing up the lamictal, starting with the "very hard to get a hold of" 2 mg tablets. As we took the depakote down, we took the lamictal up. We got to the point where his lamictal levels were in the middle of theraputic levels and the depakote was only 52. We took him down another 1/2 capsule and he began having seizures again. His neuro increased his depakote again (back up to 2 capsules twice a day, and 25 mgs lamictal twice a day) and he's doing fine. Does this mean that the lamictal won't be theraputic, or can it be normal for his body to react that way once his levels went under theraputic?