I noticed the Unoffical patch says
"Fixed the following weapons and armor not being improvable at a workbench or grindstone: ___ Ebony Blade (4838F)___"
yet if you read the book near the Ebony Blade it specifically says
"Not even the hottest fires of the Skyforge could melt it; indeed the coals themselves seemed to cool when it was placed within."
So to me it seems that having the Ebony blade unimprovable is actually intended and not a bug. While that would make the Ebony Blade not so strong as other weapons, I think the unoffical patch is supposed to be purely a bugfix, not a balance mod?