Hi Sking,
I am having this same problem and I can provide a save file for you to look at. My Durance has 11 Mechanics (I retrained him specifically after reading your comment), but I still can't detect the crystal.
The file's too big to upload directly to the forum, so I've put it here for you in a .rar: https://drive.google.com/file/d/0Bx9pQfqTBHAlcHl6ZkkyMnNHbWc/view?usp=sharing
Thanks!