Un-erasable tiles

You know when tiles branch out when you are placing them on map editor, like this?:
Annoying, ya I know.
But on the map editor, the couple of tiles just back from the border can't be placed in. These ones:
Wondering how I got 2 in there? It's because when the tiles branch out and it is close to the side like this:
It branches out all the way to the border, like this:
Thus, they are un-erasable, like this:
The only way I found of erasing them is to make the erased line branch out, which I don't have an attachment for sadly.
I actually want both the branching out thing and the border thing fixed.
Annoying, ya I know.
But on the map editor, the couple of tiles just back from the border can't be placed in. These ones:
Wondering how I got 2 in there? It's because when the tiles branch out and it is close to the side like this:
It branches out all the way to the border, like this:
Thus, they are un-erasable, like this:
The only way I found of erasing them is to make the erased line branch out, which I don't have an attachment for sadly.
I actually want both the branching out thing and the border thing fixed.