Map view of grass-dry lines

Now the second thing is that when i trye to remove them with concrete there seems to occasionally spawn in new grass dry tiles.
Before

After placing some concrete tiles

Extraweird is also that when those lines appear after a second regen of the tiles in that area the tile looks like grass, but when using the get_tile function it returns that it is a lavastone tile(not what it looks like!)

Now after some testing i think it has something to do with biome borders.
Biome in a biome(before)

Biome in a biome(after)

Notice how many lines there are!
1 Biome alone(before)

1 Biome alone(after)

Notice the no lines in the biome alone!
Further tests showed the same results. As soon as there came a new biome those lines appeared again, but as long as the biome was the same all the time. No lines appeared.
(each tile regeneration was 30 * 30 big, but sometimes 30*60 tiles big
So to conclude something doesnt seem to be right when it comes to those biome borders
