In Chapter 9, when the group confronts the invisible Duffers, the book reads:

"I don't see all your weapons," said Reepicheep.

"Are they invisible too?" The words were scarcely out of his mouth before they heard a whizzing sound and next moment a spear had stuck, quivering, in one of the trees behind them.

"That's a spear, that is," said the Chief Voice.

"That it is, Chief, that it is," said the others. "You couldn't have put it any better."

"And it came from my hand," the Chief Voice continued. "They get visible when they leave us."

Yet in the very next chapter, Chapter 10, The Magician's Book, the second sentence reads:

It was very funny to see the plates and dishes coming to the table and nothing carrying them.

However,

in the previous chapter objects became visible when they left the duffers, yet here they were still visible while the Duffers carried them.