Floodfill doesn't work on trim terrains

[NQNStudios]

Floodfill modifies terrain as it goes, triggering retrimming on terrain fringes. This closes off connections between contiguous same-terrain tiles, so you don't get the floodfill you expect. You get a narrow cross with its center where you click.

[clort81]

two stage it. 1) mark tiles for change 2) change tiles.