I'm not 100% sure if this is yet another EMU glitch or not but. If you dual-wield and you sharpen both weapons (only equipping 1, sharpening, then unequip, equip other, sharpen, then dual-wield) I got a +4 and +4 on both weapons. However under stats it registers as +8 on each weapon giving me a grand total of +16 damage instead of +8 damage. This is probably going to get [EMU] tagged too, but hey, i'm trying.
EDIT: Added yet another EMU tag