The splitting issue is just the way the editor handles B-E sheets. When viewing them in an image editing program, the sheet is 768 x 768. But the editor splits it in half vertically, putting the right half under the left half. This is likely so that it fits into the tileset viewing area. You can use an image editing program to fit them into the sheet so that it doesn't get split, or, just scroll down and select the other half and place it.