Using CustomProperties from .blend files?

Hi. I'm making my levels in Blender, and this requires me to mark some geometry objects with special properties (for example, I want some walls to be bombable, some cubes should kill the player when touched, etc.) My plan is to mark these objects with a custom property in blender, and then have a script in Unity that interprets these properties and attaches components to the object accordingly. Unfortunately, the OnPostprocessGameObjectWithUserProperties event that I'm using to do this doesn't seem to be triggering at all.

Here is my code.

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 using System.Collections.Generic;
 
 public class LevelPropertiesPostProcessor : AssetPostprocessor
 {
 
     void OnPostprocessGameObjectWithUserProperties(GameObject go, string[] propNames, System.Object[] values)
     {
         Debug.Log ("processing properties.");
 
         //Loop through every custom property and run its method
 
         for (int i = 0; i < propNames.Length; i++)
         {
             if (LevelPropertiesMethods.propertyMethods.ContainsKey(propNames[i]))
             {
                 LevelPropertiesMethods.propertyMethods[propNames[i]](go, values[i]);
             }
         }
     }
 }
 
 public static class LevelPropertiesMethods
 {
     public delegate void PropertyMethod(GameObject go, System.Object value);
     public static Dictionary<string, PropertyMethod> propertyMethods = new Dictionary<string, PropertyMethod>();
 
     static LevelPropertiesMethods()
     {
         //Populate the property methods
 
         propertyMethods.Add ("non-convex", NonConvex);
     }
 
     //Property methods
     public static void NonConvex(GameObject go, System.Object value)
     {
         //Make the object non-convex
         go.AddComponent<DontMakeConvex> ();
     }
 }

The Debug.Log doesn't even print. What could be wrong?