Mantis#1746. Thank you kindly, nlin & M.Igarashi for a patch that:

Dot product operator in LSL_Types.cs incorrectly returns a 
component-wise vector multiplication; it should return a scalar 
dot product. Thanks to M. Igarashi for the patch.

OpenSim/Region/ScriptEngine/Common/LSL_Types.cs

@@ -141,9 +141,9 @@ namespace OpenSim.Region.ScriptEngine.Common
                 return new Vector3(lhs.x - rhs.x, lhs.y - rhs.y, lhs.z - rhs.z);
             }
 
-            public static Vector3 operator *(Vector3 lhs, Vector3 rhs)
+            public static LSLFloat operator *(Vector3 lhs, Vector3 rhs)
             {
-                return new Vector3(lhs.x * rhs.x, lhs.y * rhs.y, lhs.z * rhs.z);
+                return Dot(lhs, rhs);
             }
 
             public static Vector3 operator %(Vector3 v1, Vector3 v2)

OpenSim/Region/ScriptEngine/Common/LSL_TypesTestVector3.cs

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) Contributors, http://opensimulator.org/
+ * See CONTRIBUTORS.TXT for a full list of copyright holders.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the OpenSim Project nor the
+ *       names of its contributors may be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+using System.Collections.Generic;
+using NUnit.Framework;
+using OpenSim.Tests.Common;
+using OpenSim.Region.ScriptEngine.Common;
+
+namespace OpenSim.Region.ScriptEngine.Common.Tests
+{
+    [TestFixture]
+    public class LSL_TypesTestVector3
+    {
+        /// <summary>
+        /// Tests for Vector3
+        /// </summary>
+        [Test]
+
+        public void TestDotProduct()
+        {
+            // The numbers we test for.
+            Dictionary<string, double> expectsSet = new Dictionary<string, double>();
+            expectsSet.Add("<1, 2, 3> * <2, 3, 4>", 20.0);
+            expectsSet.Add("<1, 2, 3> * <0, 0, 0>", 0.0);
+
+            double result;
+            string[] parts;
+            string[] delim = { "*" };
+
+            foreach (KeyValuePair<string, double> ex in expectsSet)
+            {
+                parts = ex.Key.Split(delim, System.StringSplitOptions.None);
+                result = new LSL_Types.Vector3(parts[0]) * new LSL_Types.Vector3(parts[1]);
+                Assert.AreEqual(ex.Value, result);
+            }
+        }
+    }
+}