Mantis#2354. Thank you kindly, Tglion for a patch that:

The average-value of modify.ModifyBlock.Height in LLClientView.cs:4170 
seem to be incorrect or it isn't the average? Mhhh...
So the terrain build -> Flaten Sphere is unuseable.
I have put in a patch that contains a workaround while 
the main problem is not solved.

2 files changed, 25 insertions, 0 deletions

diff --git a/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs b/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs
index d2f46e5..b2138aa 100644
--- a/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs
+++ b/OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs
@@ -4179,6 +4179,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                                     handlerModifyTerrain = OnModifyTerrain;
                                     if (handlerModifyTerrain != null)
                                     {
+                                        modify.ModifyBlock.Height = -1; // Hack, i don't know why the value is wrong
                                         handlerModifyTerrain(modify.ModifyBlock.Height, modify.ModifyBlock.Seconds,
                                                              modify.ModifyBlock.BrushSize,
                                                              modify.ModifyBlock.Action, modify.ParcelData[i].North,
diff --git a/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/FlattenSphere.cs b/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/FlattenSphere.cs
index e507481..c103d99 100644
--- a/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/FlattenSphere.cs
+++ b/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/FlattenSphere.cs
@@ -40,6 +40,30 @@ namespace OpenSim.Region.Environment.Modules.World.Terrain.PaintBrushes
 
             int x, y;
 
+            if (rz < 0) {
+                double sum = 0.0;
+                double step2 = 0.0;
+                duration = 0.009; //MCP Should be read from ini file
+
+
+                // compute delta map
+                for (x = 0; x < map.Width; x++)
+                {
+                    for (y = 0; y < map.Height; y++)
+                    {
+                        double z = TerrainUtil.SphericalFactor(x, y, rx, ry, strength);
+
+                        if (z > 0) // add in non-zero amount
+                        {
+                            sum += map[x, y] * z;
+                            step2 += z;
+                        }
+                    }
+                }
+                rz =  sum / step2;
+            }
+
+
             // blend in map
             for (x = 0; x < map.Width; x++)
             {