
So that first image, the red circled bit is where I originally wanted my corner post. I stopped building the wall segment one tile before that circled area then chose to build a cornerpost. but instead of placing the cornerpost there it extended the fence by one tile THEN added the cornerpost, which I was not expecting.
So anyway I re-paved the ground leading down to where the other corner post was going to be and continued building. When I got to where I wanted my next corner post I remembered what had happened so I stopped building the fence 2 tiles before where I wanted my corner, and this fucking happened:

So you can see the tiles on the other side of the fence, that's where I wanted the palisade to go, but when I chose to build the corner post at the red circled bit, this time it did not extend the fence by one tile, it just built it right where I chose.
WTF! is it one rule for horizontal placement and one for vertical? What gives? How come the first time when I chose to place a corner post it extended the fence by one tile but the second time it didn't?
I'm worried about getting my end corner post to line up with my initial one.
Any advice?