User blog comment:AbigailAbernathy/Mephala's Ebony Blade in Skyrim./@comment-3492791-20120817074231

Not a bug. Some items just can't be improved for whatever reason. If you read the book on it it actually mentions that it can't be damaged. Thus you can't sharpen it, since that would be damaging it in a way.

DarthOrc's mention of friend killing will only improve the enchantment to do more damage, not the physical damage value.

Also, as partly mentioned, it is a two-handed weapon and use it levels up the two-handed skill, but it effectivly functions as a one-handed one and one-hand governs the damage. THIS is a bug.

If you aren't skilled in one-hand, I would advise against using it.