I'm having this same problem, on bios version 0129.
Glad to find out I can regain that lost gb by switching back to auto. (not that I was tweaking voltages or anything, just setting it from the detected 5-5-5-18 timing to the ram's ACTUAL 5-5-5-13 timing).
I must say I'm quite bewildered by this product. SO many features, most of them very nice and rare.. but so many silly problems with the bios it's almost not worth it