When you make a ghost stable rune, it will appear as a ghost, but it would have collision. This might be due to the stable rune being designed off of the regular rune, which in its 'ghost' form has collision, but the textures of the stable rune were never swapped for this feature.

I noticed this too, it's annoying and confusing when a shaman uses it, I never know if it's ghost or not. Hope it gets fixed someday...