I've just tried it on my 590/5 and it does exactly the same thing.
That’s odd as it doesn’t do it on my Nav V.
Here is what I did.
I recreated your route A6034 > Priory Hospital Keighley > 53 Skipton Road, as nearly as I could in my Nav V. I didn’t create the route in BaseCamp or anything like that.
The first time I did it in car mode, fastest time, with the hospital as a favourite (orange flag)
The displayed route was fine.
I then changed the hospital into a shaping point (blue dot)
This brought on the inevitable recalculation
but again the route was fine
The only difference being that (not surprisingly) the yellow flag has vanished, only the heart remaining. This did not surprise me as I had saved the hospital as a favourite in my device, simply to make it easier to create the A to B to C route.
I then drove the route in simulation mode. As I expected, it drove perfectly, leaving the start on the A6034, straight ahead at the roundabout, crossing the A629
driving on to the hospital, where (as expected) it spun around.
The position cursor then retraced its steps, back the way it had come, correctly following the route
back to the roundabout, where it dutifully turned left on the A629 and then drove to the end point at 53 Skipton Road.
I then changed the mode to off road and ran the same route twice. Once with the hospital as a viapoint (orange flag) and once with it simply as a favourite (blue dot).
Each time it behaved perfectly, despite inevitable recalculations when between switching modes and then switching between the qualities of the hospital.
In short, it all behaved exactly as it should do and exactly as I expected it would. I would have been happy to drive all and any of the routes in real life, confident that the real life experience would match that of route simulation.
I then wondered if, as I had created the hospital as a favourite, whether that made any difference.
I deleted the hospital from my favourites and deleted to A to B to C route. To all intents and purposes my device was clean.
Again, in car mode, fastest time, I asked the device for a route but this time, just A to B, A6034 > 53 Skipton Road, which it did perfectly
I then asked my device to find me a hospital near the route, which it did
As it’s the same hospital as we have used before, I asked the device to insert it into the route. This it did with the inevitable recalculation
The offered up route was perfect, the hospital midway as I expected it to be, marked by an orange via point flag
I then asked the device to change the hospital into a shaping point (blue dot). Again, this required a recalculation to be performed but the end result was again, perfect. The orange flag had simply been replaced by a blue, shaping point, dot
I can offer no logical explanation as to why your XT AND your 590/5 differ so dramatically from my Nav V. I certainly can’t replicate it. Switching the qualities of a predetermined point between a favourite, a via point and a shaping point should not (despite recalculation) alter a route’s path A to B to C. Certainly the placement of the point should not move, nor should it be missed out.