How do you clear a player's Transmutation Tablet data?

[Teraku]

I'm running a server with EE enabled, and one player would like to start over, and also have his Transmutation Tablet data removed.

But for some reason, I can't delete his Transmutation Tablet data. I go into the world/Data folder, and delete the tablet_(name) file of that player, while he is not in the server. I then restart the server, and the file is still gone. But when he opens his Transmutation Tablet, it still knows everything. Before I cleared his data, he did use an Alchemical Tome on the table, though. Maybe that could affect it.

How do I permanently delete this guy's data?