Can be seen when placing a tree-farm with fences in its bounds -- it will remove all of the fence blocks that are connected.

Makes it difficult to adjust bounds on a tree farm, as it will start to eat up the fences if you mis-adjust the bounds, as well as it seems to cache target blocks to clear even if they are no longer within the bounds.

On bounds adjust - clear all cached work targets and start rebuilding from zero with usual incremental scan. Make clear note of this in instructions that it will invalidate any in-progress work.