Miscounted overlay rows

[temnix]

I'm making an area from a copy of an existing place, whose graphics I edited a great deal. The area ends up looking scrambled in Near Infinity and in the game. Could this be because the original's WED file lists a wrong number of tile columns - 57 instead of 58 (I added a column to the area to beef it up on one side)? No matter how many times and in what manner I convert the PNG file for the area into TIS, whether in Beamdog's format or in the large original, the WED continues to claim that this overlay's width is 57. If the TIS is loaded in DLTCEP and the "Guess dimensions" button is used, the right number of columns appears along with the sizes, but saving the tileset doesn't fix this information in place. At least that's my guess about the scrambled representation. Any ideas?