Comment 1 for bug 451304

From downstream report:

  "According to the web site listed, partition type 0x12 (Compaq diagnostics) is also used by Thinkpads for the recovery partition. I can confirm this, at least on my Lenovo X200 Tablet. Adding 0x12 to the hidden partition types would hide the recovery partition by default, which I consider to be a bonus: a technically minded user can always unhide the partition if they need access to it. As I've already hidden mine with a custom rule, I don't mind either way."

Indeed http://www.win.tue.nl/~aeb/partitions/partition_types-1.html lists 0x12 only for configuration/rescue.