Mantis#1521. Thank you kindly, Lmmz for a patch that:

Improves the implementation of the particle system.

OpenSim/Region/Environment/Scenes/SceneObjectPart.cs

@@ -1056,6 +1056,11 @@ namespace OpenSim.Region.Environment.Scenes
             m_particleSystem = pSystem.GetBytes();
         }
 
+        public void RemoveParticleSystem()
+        {
+            m_particleSystem = new byte[0];
+        }
+
         /// Terse updates
         public void AddTerseUpdateToAllAvatars()
         {

OpenSim/Region/ScriptEngine/Shared/Api/Implementation/LSL_Api.cs

@@ -4322,11 +4322,34 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api
             return returnval;
         }
 
+        private Primitive.ParticleSystem getNewParticleSystemWithSLDefaultValues()
+        {
+            Primitive.ParticleSystem ps = new Primitive.ParticleSystem();
+            
+            // TODO find out about the other defaults and add them here
+            ps.PartStartColor = new LLColor(1.0f, 1.0f, 1.0f, 1.0f);
+            ps.PartEndColor = new LLColor(1.0f, 1.0f, 1.0f, 1.0f);
+            ps.PartStartScaleX = 1.0f;
+            ps.PartStartScaleY = 1.0f;
+            ps.PartEndScaleX = 1.0f;
+            ps.PartEndScaleY = 1.0f;
+            ps.BurstSpeedMin = 1.0f;
+            ps.BurstSpeedMax = 1.0f;
+            ps.BurstRate = 0.1f;
+            ps.PartMaxAge = 10.0f;
+            return ps;
+        }
         
         public void llParticleSystem(LSL_Types.list rules)
         {
             m_host.AddScriptLPS(1);
-            Primitive.ParticleSystem prules = new Primitive.ParticleSystem();
+            if(rules.Length == 0)
+            {
+                m_host.RemoveParticleSystem();
+            }
+            else
+            {
+                Primitive.ParticleSystem prules = getNewParticleSystemWithSLDefaultValues();
                 LSL_Types.Vector3 tempv = new LSL_Types.Vector3();
 
                 float tempf = 0;
@@ -4467,6 +4490,7 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api
                 prules.CRC = 1;
 
                 m_host.AddNewParticleSystem(prules);
+            }
             m_host.SendFullUpdateToAllClients();
         }