Map appears rendered with a grid

[svera]

When rendering a map, this is shown with a grid delimiting each of its tiles.

For an example, check level11.zip

[aerth]

seems to be related to tileset margin, changing the level11 map to margin=2 seems to make the grid disappear but then introduces a weird offset that cuts of the top-right of each block

but then i open the tileset image in gimp and notice that the tiles are 18x18 with 0 margin and 0padding, not 16x16. (map's tile size to 18x18, and changing the tileset image's tile size to 18x18)

are we sure this map should render properly (as it exists now)?