I don't know whether HHG was at the World's End or not, but I found a similar issue in the area around coordinates (-83,-5).
I was going down the river by boat, and suddenly I found out that I could not go beyond some invisible east-west line. I tried to trespass it by going through the woods, but it extended on both water and land. Thinking that it was some bug with map tiles, I tried to find the end of the "invisible barrier" by following it to the east: after a while I found a corner, after which the barrier continued in north-south direction.
The red lines in the image below represent the two sides of the "barrier" I could find, before deciding it was time to go back home

It's not a big issue for me since my character lives quite far away from this place, but I thought it was worth mentioning the problem in the forum...
