Fix

src/com/t_oster/liblasercut/VectorCommand.java

@@ -61,6 +61,7 @@ public class VectorCommand
   {
     if (type == CmdType.SETPROPERTY)
     {
+      this.type = type;
       this.property = p;
     }
     else

src/com/t_oster/liblasercut/VectorPart.java

@@ -41,8 +41,13 @@ public class VectorPart
 
   public VectorPart(LaserProperty initialProperty)
   {
+    if (initialProperty == null)
+    {
+      throw new IllegalArgumentException("Initial Property must not be null");
+    }
     commands = new LinkedList<VectorCommand>();
-    this.setProperty(initialProperty);
+    this.currentCuttingProperty = initialProperty;
+    commands.add(new VectorCommand(VectorCommand.CmdType.SETPROPERTY, initialProperty));
   }
 
   public LaserProperty getCurrentCuttingProperty()