This isn't techniqually working as intended.
The INTENDED way of Raise Ghoul is to raise ONE Ghoul to fight along side you. Using Dancing Rune Blade thus gives you ANOTHER Ghoul along side you, obviously the part where it is 'Not Working Intended' is in the 'Raises one Ghoul to fight along side you'.
However, the Dancing Rune Blade also states 'Uses the same abilities as the DK', so it could also be intended. None the less, I didn't know this, and I will +rep you for finding and informing me.