I've observed that once u acquuire crystallize skill on dwarf you no longer can destroy C and D items for beginners. And since there is a lot of those items you end up in cluttered half of inventory.
On trying to destroy or crystalize you get the same error: "this item cannot be crystalized".
Char name: Digger
http://forum.dragon-community.net/index.php/topic,290114.0.html