I think i found also the bug with the strange heightmap scratches.
The scratches appear, when there are 2 spline points too close to each other.
For example: if you click the “Add End” Button and dont move the second spline point, but add a third spline point, then there will be a scratch starting at the 2 very close spline points.
So if you have a minimum distance between each spline point, then there will be no scratch in the landscape
Thanks for the great tool! i like working with it and hope i can help you fixing the last bugs 