[DustyPorViva]

Gonstruct defaultly has pics1.png as a tileset that applies to all levels. The problem is that Gonstruct applies priorities chronically instead of by prefix. That means nonspecific tilesets like the pics1 will overwrite specific tilesets for levels if they are higher on the list. This is pretty annoying and actually breaks the ability to use tiledefs.

To fix this, what you can do is add your tileset, remove the default pics1 tileset, then add the pics1 tileset back with a blank prefix. This will put your tileset at the top of the list, making it a higher priority. You'll have to do this every time you add a tileset.
Be very careful when messing with tilesets because if Gonstruct can't find a tileset with a blank prefix, it will crash, making it hard to get working again.

If you'd like, I can possibly eventually make a tutorial video now that I can record stuff.