By "IFR approach" do you mean requesting an ILS/LOC/GPS/VOR/NDB approach while VFR?
If so, a controller making you IFR prior to issuing an approach instruction (without you specifically requesting a pop up) is a bit odd. Matter of fact, I'd be willing to bet there is not one single controller in my building who would make a VFR aircraft IFR unless the pilot specifically requested a pop-up IFR, when coupled with a practice approach. We do it all day, every day:
VFR aircraft: Request vectors for the ILS into (airport).
Us: Roger, fly heading xxx, vectors for the ILS, maintain VFR.
Now, if a VFR aircraft called up and asked for "an IFR approach into (airport)" I'd take a few seconds to determine what, exactly, the pilot was asking for before proceeding. And that would include a very specific query as to if the pilot wanted a practice approach VFR or wanted an IFR clearance.
All that aside, I'm not sure why you would have to cancel after conducting a VFR practice approach. You're not IFR, so there's nothing to cancel. Different strokes for different folks on that one - or, maybe there was some confusion on the status (VFR/IFR) of the aircraft as they got handed from controller to controller. That, I have seen happen.