Good news, Garry.
It may not be exactly what you want to hear but, like others, I think your XT is behaving in exactly the same way as most reasonably modern Garmin devices do and certainly exactly as both my Nav V and Nav VI do. To test it out I did nothing more than ride my bicycle for several miles, around the streets of east London.
This is how I did it:
1. I first created a 5.4 mile A (home) to B (in Islington) route in Basecamp. This was a route, not a track or anything like that. To make it in a way representative of a longer day out type route, I made it very complicated, including a fiddly twiddly loop in a full circle around some narrow City of London alleys. In short, something difficult for the device to replicate and something that I would definitely notice had been changed through recalculation at any point
2. To guarantee I took the small City alleys, the route had shaping points, but no waypoints between A and B. This way it gave the two devices no additional help at all beyond shaping points
3. I left my house but first ensured that the route, as I was within inches of my front door A, would run properly. I fired up both devices and was (not unsurprisingly) presented with the simple choice, would I like to go to A or B. I chose B, the end point. On both devices the route displayed and functioned normally. I could ride it the 5.4 miles from A to B, around all the twiddly bits and the loop with 100% confidence
4. I then turned the routes off on both devices by stopping them, touching the 'X' button. On one device I went bit further still and turned it off completely with a long hold on the power button. In short, neither device could be running my route. They were both not active, one to all intents and purposes dead
5. I then deliberately rode my bicycle a mile away (in completely the wrong direction) from the route and stopped
6. I then fired up both devices again, went into Trip Planner and summoned up the route. I was, again, not surprisingly presented with the choice of the only two possible destinations, A or B
7. I chose B on both devices. Not surprisingly and just like your XT, both devices calculated me a fresh route from where I was standing to B. The route (again not surprisingly) was nothing like my wiggly route through the alleys of the City of London. It went direct to B. In a word, useless
8. I then stopped the route on both devices, turning one fully off again
9. Then I fired both devices up again and summoned up the route once more
10. I did not activate the route by hitting GO on either device. What would be the point? I know that I would only be presented with the same choice A or B and an inevitable recalculation which I do not want to see
11. Instead of hitting the GO button, I pushed the Map button. This brought up the magenta line of the still inactive route and showed my position about a mile off it
12. I zoomed the map in and out a bit to find a road to take so that I would meet the magenta line about half a mile from my house, well before the twiddly trip around the City of London's alleys and still about 5 miles short of the end destination, B
13. Using the screen as nothing more than a dumb map, I rode to meet the magenta line. In other words, doing the equivalent of: “Please drive to the highlighted route”. Please note, the map on the screen does not scroll in this mode of use but the position icon does move, just as you'd expect it to. To make the map scroll, drag it by hand or use the + / - buttons to zoom in and out
14. I arrived smack bang on the magenta line
15. I then used the back button to take me back to the device's routes' screen
16. This time, on both devices I pushed GO and was give the bog standard choice, A or B. As I knew I was standing on the magenta line and the position marker showed that I was, I chose B on both devices and.....
17. BINGO, again! Both devices display my homemade twiddly route (including all the little alleys) perfectly, giving me the routing direction from where I stood (I wasn't at the start point don't forget) for the next nearly 5 miles to B in Islington. A perfect double result, from two separate Garmin devices
18. Just to be very sure, I didn't move my position but I again stopped the route on both devices, turning one device right off. Nether device is now doing anything, one is fully dead. I short, they were little more than two plastic box of widgets. I might as well have been asleep in my bed at home, ahead of continuing the route the next day
19. I then fired up both devices again and summoned up the complex route. I pushed GO on both device, selecting B, from the usual simple two destination choice
20. BINGO! again. As I was stood on the magenta line both devices displayed and ran the twiddly route all the way to B
21. I then tried Lee's suggestion of inserting an additional waypoint along the route, using nothing more than the device's screen. Basically, I zoomed in on the route, touched it where I wanted to place the point. The point it is created as a waypoint by default, though it can be converted to a shaping point if required from within the device itself (see 23 below)
22. The device made a recaclution, inevitably but the route as a whole remained true
23. I stopped the route again and summoned it back up again. This time I was looking at three choices of destination: A (home, my original start point), a new B (the freshly created new waypoint) and C, my original end point. I could navigate to each with ease and absolute accuracy. Please note, when inserting fresh waypoints into a route, say for a fuel station, you need to be careful where in the route list it goes. This is editable via hitting the three horizontal bars in the top left corner of screen and hitting the Edit Destinations choice. This is a really useful screen as you can change the position of shaping and waypoints and change a waypoint into a shaping point and visa-versa. Each change will necessitate the device making a recalculation but it should be quite safe, depending on the device's preference settings. I have all mine turned to all but off, so the changes if any are usually small
24. On each device the recalculated route displayed and ran perfectly, true to the original
As far as I can tell and as far as is sensibly possible I have replicated the challenges you faced. In all this I fully appreciate I am not holding an XT in my hands. But, that being said, I can - through doing nothing more than operating two separate, reasonably modern, bog standard Garmin devices in their usual way - replicate (with no effort at all)
exactly the problems you see on your XT, overcoming them without too much difficulty and certainly without fiddling about creating routes, converting them into tracks and then back again into routes. I am as confident as I can be that, had I been holding an XT, I could have done exactly the same, with exactly the same good results.
I have done all the above with the best intentions of helping you. If all this is nothing more than a lucky, twice occurring, separate coincidence on two separate devices and the XT you are holding is very different or in need of software fixes (or a belt with a hammer) so be it. However, I am struggling to believe that it is or can be. My only conclusion is that your XT is performing, not as you expect it to, but exactly as Garmin intends it should, all along. I am happy to hear news and views.
All the best, stay well!
Richard
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