It's bugged don't feed us some bull crap it was intentional without a source.
I though it was a bug too until I opened its template with the CK.
The way it works (not only the attributes but also its DPS, which is typical of a one handed weapon) makes me think it was intentional. There's also a different ebony blade in the test cell: also that one has the same characteristics despite a different enchantment.
So, it was either intentional or whoever did that was seriously drunk!