I've been working on the GPS files..
At Newbridge on Wye, between Builth and Rhayader there is a right turn on a B road that goes nowhere, and then comes back again - it isn't on the route sheet. I don't think it's the 'new road' mentioned by Mark above, as it reverses on itself...
Looks like a 'mistaken click' when preparing the route, (one which looks like it's on the main road, but is actually a bit off to the side, causing an out and back detour), so probably can be deleted, though it is, of course, your decision, not mine !!
There's another one up and back on Pehrhos Road, either before or maybe just after the Menai Bridge (it is an obvious 'tag' when viewed..)