Hi David.
I've given up over Bookmarks and have lost all my remembered passwords etc, ets.

(
Anyway, I have been messing about a bit more. All the problems seem to have been fixed except that I have found three small snags.
1a. The round symbols disappear once they have been dragged onto a tile unless one goes to 1:3 Zoom. At 1:5 (my working zoom) they are completely invisible. Can I suggest thickening, and brightening slightly, the two arcs (and, possibly, bring them a bit closer to the 'centring' dot.
1b. Removing a 'dot' seems to involve dragging a box around it, disconnecting the symbol, boxing it again and, finally, doing delete. Is that the correct procedure. Just right clicking it comes up Set Position.
2. I wanted to add in a whole new row of tiles at one point so did a series of joint disconnects to seperate the two parts of the layout. When I started adding in the new tiles, they joined part one OK but when I tried to offer up part 2 it would not join up. I carried on anyway and by the time I had finished it had sorted itself out. I'm not sure exactly what happened and I'm not trying again!
3. Are you working on a diagonal buffer section?
BTW, my thanks to Sander who was talking about 'flipping' tiles; I hadn't noticed that.
Other than that, I'm a happy bunny, as they say. If I come up with any further problems I'll let you know.
All the best,
Chris