After upgrading the BIOS to 0156 something is wrong at fan control in BIOS Menu.
If I change in "Configuration->Fan Control" the value for "Minimum Duty Cycle" for "Front Fan Header" it happens changed for the Rear Fan Header. If I change the value for Rear Fan Header the same thing happens for Front Fan Header.
They are exchanded since 0156.
Default settings loaded after flashing.
I understand that after you updated the BIOS to version 0156, the front and rear fan controls switched and now the front fan reading is for the rear and vice versa.
I recommend you to contact your local support and create a case to try to replicate the problem.
Here is the contact information:
We would like to inform that we tested with BIOS versions 0151,0155 and 0156 and we are not able to duplicate the issue in our demo systems. All front, back and rear fans work fine even when stopping them with a finger reason why we recommend to reset BIOS to its default settings and to perform BIOS recovery to version 0156 using F7 after loading BIOS defaults:
http://www.intel.com/support/motherboards/desktop/sb/cs-022312.htm Desktop Boards — BIOS update instructions