Interestingly it doesn't happen in the Narnia books, IIRC - at least in Lion, Witch & Wardrobe the Professor turns out to remember his own trip to Narnia very clearly..

But by the Last Battle Susan thinks it was all lets-pretend.

And there is a tendancy in Narnia for Aslan to turn round and say "Aha! You're not getting back this way", even though they worlds arn't sealed apart. In fact, given that Narnia is utterly destroyed in the last book, that's a pretty drastic perminently sealing apart, in at least some ways.