Functions such as TCOD_tileset_load will load tilesets in a way where the first tile is not rendered.

I assume this is because the first tile is loaded into tile index zero, which is special cased by several functions. The tileset will correctly map the codepoint to zero, then the special case will take over and the foreground will be skipped.

An important note is that the first tile is also used to detect the background color. So fixing this might cause tilesets to be loaded without a resolved alpha layer, causing background colors to be ignored.