I've been having some problems with my map maker before when making maps, but i had previously assumed it was becasue i was experimanting with making rather large maps. But just now i have made a new heightmap and put it into the mapmaker, and it instantly glitched how it has been on the larger maps.
Things that have been happening include:
A Boundary-ish area going around the edge of the whole map, maybe about 5-10 % areound the edges of then where if i walk over there when testing it, i will fall into the ground. I'll usualy be able to see this area beacuse there will be an extremely faint line on the ground.
Large "Walls" Appearing around the map edges" They dont affect the map much, but they definately shouldnt be there.
Random floating chunks of land, these are irritating and hard to explain, but you will see in the image i've uploaded. sometimes these are stuck partly inside the map, messing it up, and sometimes they are simply floating next to it.
And Finaly, something that has just appeared with my new map, chunks of the map itself are being cut off around the edges.

Screenshots:
The first 2 show how some of the map edges have been cut off.
The second 2 show a "Wall".
The next 2 show Part of the wall and the floating land.
The last 2 show some "Walls" that are on my larger map.
I am mainly wondering if anyone else has encountered this, and if so, is there anything i can do to correct it other than reinstalling the game.
As a final note, i'm pretty sure I haven't edited any of the game files other than downloading and making maps and presets.