I believe that what you're seeing there is purely the information about the RAM type in that particular slot. It's like a label on a carton of cigarettes: The label may state "20 x Look 100's", but if you check the contents you may find that there are only 18 cigarettes left. The analogy is bad, but I hope it gets my point across.
So let's look into the actual settings of your RAM.
What you want to look for is found in "Advanced Mode", and is likely labeled something like "DRAM Speed", "DRAM Frequency" and "BCLK : DRAM Frequency Ratio". Could you tell me what you find there?
Besides: You do not need to downclock your RAM manually from 1600mhz to 1333mhz. The motherboard has right of way, so to speak, and it will decide on it's own.