I believe this is either a limitation of one of the following -
Processor; etc and maybe something to do with SPD though most memory should have this today.
Here is the original Board Specification, however, the latest update has nothing new about Ram
This is rather unfortunate.
Socket 1156 Accepts 1Gen i3's, i5's and i7's Mainstream CPU's with the memory Controller inside the CPU itself.
This specific memory controller can Handle up to 16GB DDR3-1333MHz. This is by design i am afraid. So there is no other way you can bypass this limitation. Sorry.