By the time Lindell/Pharek's secret lab had been found, the damage to the hidden room had been repaired by the protective arrays of the palace. The complex and delicate instruments were intact, but too many things were out of place.
The Forge had disappeared, leaving only a depression in the carpet. The many books scattered throughout the room and the several empty shelves were the only remaining signs of struggle.
No mage would be foolish enough to set up an array to put books back in their place.
Otherwise they wouldn't be able to read without the array taking the tome off their hands like an annoying librarian. If a shelf had been broken, the books were right below it.
If a spell had blown it to bits, however, the explosion would propel the books away.