After a really long time, I figured it out: some tiles apear as normal plain grass and nothing seems wrong but when tried to dig furrow or a grave, they will not work.
This was very anoying for me because I just wanted to farm and for some reason, I couldn't.
Now, please show these as actual gravel tiles, or remove them but don't show grass on a tile that is not grass.
See video for clerification.
PZ2.mp4