It is the case with all the special weapons that the skill is still effected when you swap bars.
One issue is, if the skill hits the target after the weapon swap the effect does not occur. This is the case with damage weapons and since heals do have a travel time I expect it is the case as well.
Alcast demonstrated this with the vAS destroy and that if the force pulse hit the target when on the other bar the effect would not occur. iirc he said it was the case with other special weapons as well.
With that, I have never experienced an issue with the vMA rstaff not procing regardless of what bar I am on.